Taskbar, menu and window titles sometimes don't scale

I set “Custom DPI Setting” in dom0 settings (XFCE) to 144. This used to work fine, but recently, sometimes when I start Qubes the DPI setting will not be applied to the taskbar, menu and window titles. Everywhere else (i.e. inside windows, such as dom0 terminal or settings) it will always work. This will really only happen 50% of the boots though, the other times everything scales fine.

On a boot on which the scaling is not working properly, changing the “Custom DPI Setting” or the “Window Scaling” setting to various values doesn’t affect the taskbar, menu and window titles at all. Whereas on a boot with functioning scaling the values have immediate effect.

I can’t find any related messages in dmesg, Xorg.0.log or journalctl. Also no noticeable difference in those logs between a boot on which scaling works properly and a problematic boot.

Any suggestions on how I could debug this further?