Thanks. That indeed confirms the 99.98Hz mode has suddenly gone missing in the last attachment. The system seems to be treating that as a different monitor configuration and will revert to defaults (which is landscape and 59.97Hz).
When this happens though, the monitor's EDID does not change. It still reports the 99.98Hz mode exists: Detailed mode: Clock 543.500 MHz, 797 mm x 333 mm 3440 3488 3520 3600 ( 48 32 80) 1440 1443 1453 1510 ( 3 10 57) +hsync -vsync VertFreq: 99.982 Hz, HorFreq: 150.972 kHz So if the mode exists but is not offered as an option then that suggests the kernel or driver thinks there's not enough bandwidth or a good enough connection to support that particular mode. Therefore, please try a different monitor cable. ** Summary changed: - Display orientation resets on reboot with USB-C (DisplayPort) external monitor and refresh rate dropdown disappears when setting it sometimes + 99.98Hz display mode is sometimes missing on USB-C (DisplayPort) external monitor, which resets the display layout ** Package changed: gnome-shell (Ubuntu) => linux (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gnome-shell in Ubuntu. https://bugs.launchpad.net/bugs/1922540 Title: 99.98Hz display mode is sometimes missing on USB-C (DisplayPort) external monitor, which resets the display layout To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1922540/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs