In getting ready for the upcoming lemmy release, we usually deploy a test release here on lemmy.ml (the dev instance) for a few days, to discover any issues for a large production server, so other people don't have to.
We found a performance issue with this one, so we downgraded back to 0.19.3, and restored from a database backup made a few hours ago.
I apologize for the few hours of downtime that caused today.