Several years ago now. On at least two of those tries, after maybe a month or some of daily driving, suddenly the fs goes totally unresponsive and because it’s the entire system, could only reboot. FS is corrupted and won’t recover. There is no fsck. There is no recovery. Total data loss.
Could you narrow it down to just how long ago? BTRFS took a very long time to stabilise, so that could possibly make a difference here. Also, do you remember if you were using any special features, especially RAID, and if RAID, which level?