I upgraded back to 25.0.0-1 ( sudo apt install libglx-mesa0=25.0.0-1 libgbm1=25.0.0-1 mesa-libgallium=25.0.0-1 libgl1-mesa-dri=25.0.0-1 libegl1-mesa-dev=25.0.0-1 lib egl-mesa0=25.0.0-1) and restarted and immediately started experiencing the flickering again. Here’s a short video:
Focusing on the screen correctly was difficult (and I think the image host re-encoding it has made it less dramatic?) but you can clearly see the flicker at several points in this video. It happens often with playing videos, on both firefox and vlc. Moving the mouse seems to trigger it as well, as @wakest says. I watched this video several times and it flickered often every time.
Downgrading back to 24.3.4-3 (sudo apt install libglx-mesa0=24.3.4-3 libgbm1=24.3.4-3 mesa-libgallium=24.3.4-3 libgl1-mesa-dri=24.3.4-3 libegl1-mesa-dev=24.3.4-3 libegl-mesa0=24.3.4-3) again and restarting totally eliminated the flicker. I carefully watched the video again and didn’t see it once, and I haven’t noticed it at all in my normal usage on 24.3.4-3.
Thank you for filing a bug, @josch!