Recently (3rd April) after updating Mesa to 21, not all but many application was unable to render properly, including plasmashell, zoom and systemsettings5, but firefox, dolphin, konki and konsole (last two used transparency) were unaffected. Starting plasmashell from terminal didn’t produced any informative debug statement. I pulled mesa and vulkan-intel 20 from stable and problem was resolved.
I again tried to update today, along with newer update of libva-mesa-driver and mesa-vdpau, but problem persisted.
Info:
GPU: Intel HD Graphics 4400
Compositor: xrender
GPU driver: i915
New discovery:
I just notice (while writing this, to find GPU model) the GPU is reported to be llvmpipe (LLVM 11.1.0, 256 bits) in screenfetch, inxi and OpenGL renderer string of glxinfo which used to be (last seen months ago), Mesa DRI Intel HD Graphics 4400 (HSW GT2) (Collected from inxi output on 10 June 2020)
Note:
I recently tried some VNC and also using Weylus.