PSA: this is now reverted due to a missing library:
MESA-LOADER: failed to open dri: /usr/lib/x86_64-linux-gnu/gbm/dri_gbm.so: cannot open shared object file: No suh file or directory (search paths /usr/lib/x86_64-linux-gnu/gbm, suffix _gbm)
Yes, the problem persists across restarts of Epiphany. I’ve tested this after rebooting the computer, reinstalling the Epiphany snap, and even deleting some of the .cache files associated with Epiphany.
The change in Mesa probably modified some internal configuration in Epiphany/Webkit such that downgrading prevents it from running properly. That said, once the fix to this snap is pushed, it shouldn’t be an issue anymore.