I am having the same symptoms after upgrading from 6.11.5 to 6.12.2. btrfs mirror of 2 NVMe drives. I reformatted it once after the upgrade to 6.12.2 and it triggered again yesterday sometime. Docker and VMs are running on a separate btrfs mirror (/mnt/user/virtualization). /mnt/user/cache is usually what I've noticed go read-only - most of what's going through that is system backups (Time Machine, AOMEI Backupper and Windows Backup). I attached diags in case there's something similar. These issues only started after the upgrade, no other changes to hardware have been made.
phoenix-diagnostics-20230717-0759.zip