This sounds like the upstream bug... https://gitlab.gnome.org/GNOME/network-manager-applet/issues/43
...according to the backtrace with the call of nma_wifi_dialog_get_connection() followed by free(). I'm affected by this issue too (in testing), but with the connection to a hidden SSID. The issue is already solved, so there is hope for patch by the maintainer. Because this will officially arrive earliest with v1.8.22.
