black screen with mouse cursor after switching to tty and back

[xBZZZZ]

1. run picom --backend=glx or picom --backend=egl or picom --backend=xrender (no config file)
2. press ctrl+alt+f3 to switch from graphics to tty (full screen terminal wher you can login)
3. picom starts doing

   picom/src/renderer/renderer.c

   Line 517 in 6d67682

   xcb_aux_sync(backend->c->c);

4. press ctrl+alt+f7 to switch to graphics
5. xcb_aux_sync sometimes doesn't finish

what does sometimes mean?

if any of these is running unminimized then xcb_aux_sync finishes when I press ctrl+alt+f7 (no black screen, picom works fine):

• egltri_x11
• firefox
• chromium
• mpv

if any of these is started or unminimized during black screen then xcb_aux_sync finishes and picom gets unstuck and no longer black screen:

• egltri_x11
• firefox
• chromium
• mpv
• eglgears_x11
• glxgears

versions

picom	6d67682
nvidia driver	610.43.02