No elements are displayed - only a gray window appears

[gergely-j]

When LV_USE_SYSMON is disabled, basic examples don’t display anything.
The default demo project works fine as long as an animation is running, but if you return from the function analytics_create before starting the animation, nothing is displayed either.

I've got the following error in the log: lv_display_refr_timer: No draw buffer lv_refr.c:373