it is not broken, it just doesn't seem to cope with GUI window resize which seems to be on a fixed static size;
fyi. all Carla LV2 plugin GUIs do show and behave here as same as you.
not sure it's a qtractor issue though, because many other LV2 plugins on Gtk and Qt GUIs do show up at correct size and respond nicely to window resizing (eg. the calf, the vee-ones, etc.).
on the other hand, at least on my system, the Carla-Rack LV2 GUI behaves even worse on jalv and ardour6, either crashing on show or having a plain black window that cannot be resized at all.
it is not broken, it just doesn't seem to cope with GUI window resize which seems to be on a fixed static size;
fyi. all Carla LV2 plugin GUIs do show and behave here as same as you.
not sure it's a qtractor issue though, because many other LV2 plugins on Gtk and Qt GUIs do show up at correct size and respond nicely to window resizing (eg. the calf, the vee-ones, etc.).
on the other hand, at least on my system, the Carla-Rack LV2 GUI behaves even worse on jalv and ardour6, either crashing on show or having a plain black window that cannot be resized at all.
go figure.
cheers