my solution was simply to remove the package: dpkg --purge gtk3-engines-xfce
Just to help others find the issue these are the errors on the console when running pavucontrol:
(pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:36:10: The 'engine' property is ignored (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:38:23: Custom CSS properties are no longer supported. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:39:22: Custom CSS properties are no longer supported. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:41:39: The style property GtkWidget:focus-line-width is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:42:39: The style property GtkWidget:focus-padding is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:43:39: The style property GtkWidget:interior-focus is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:45:39: The style property GtkButton:child-displacement-x is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:46:39: The style property GtkButton:child-displacement-y is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:47:39: The style property GtkButton:default-border is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:48:39: The style property GtkButton:default-outside-border is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:50:40: The style property GtkButtonBox:child-internal-pad-x is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:51:40: The style property GtkButtonBox:child-internal-pad-y is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:52:39: The style property GtkButtonBox:child-min-height is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:53:39: The style property GtkButtonBox:child-min-width is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:55:39: The style property GtkCheckButton:indicator-size is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:57:39: The style property GtkExpander:expander-size is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:58:39: The style property GtkExpander:expander-spacing is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:60:39: The style property GtkMenuBar:internal-padding is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:62:39: The style property GtkMenu:horizontal-padding is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:63:39: The style property GtkMenu:vertical-padding is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:65:39: The style property GtkPaned:handle-size is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:67:39: The style property GtkRange:slider-width is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:68:39: The style property GtkRange:stepper-size is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:69:39: The style property GtkRange:stepper-spacing is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:70:39: The style property GtkRange:trough-border is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:72:39: The style property GtkScale:value-spacing is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:75:39: The style property GtkScrollbar:min-slider-length is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:78:39: The style property GtkToolbar:internal-padding is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:79:39: The style property GtkToolbar:space-size is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:98:13: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:122:35: The style property GtkWidget:focus-line-pattern is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:131:17: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:131:37: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:157:36: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:181:23: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:198:24: The :inconsistent pseudo-class is deprecated. Use :indeterminate instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:207:77: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:216:35: The style property GtkWidget:focus-line-pattern is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:225:18: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:225:38: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:253:17: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:275:30: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:352:21: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:394:17: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:394:40: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:436:20: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:451:35: The style property GtkWidget:focus-line-pattern is deprecated and shouldn't be used anymore. It will be removed in a future version (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:460:19: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:483:22: Custom CSS properties are no longer supported. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:496:30: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:496:62: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:521:28: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:521:58: The :insensitive pseudo-class is deprecated. Use :disabled instead. (pavucontrol:1527): Gtk-WARNING **: Theme parsing error: gtk.css:537:22: Custom CSS properties are no longer supported.
