I'm using GTK emacs 26.3 on GNOME 3.34 using X.
When emacs is fullscreen, ibus-libpinyin is unable to render the pinyin suggestions. Input seems to still be working (i.e when I press a number a chinese character appears) but the suggestions fail to appear.
This problem doesn't happen when emacs is not full screen.
As a side note, rendering works when firefox is full screen, so the problem is not in all full screen apps.