As someone who is in the middle of pulling apart a BTRFS volume by hand (read: writing code to interpret the data structures) to try and recover it, I think being burnt enough is once.
No indication of any hardware issue: No recent power loss (& it's on a UPS), no SMART issues, no memory test positives. But the block tree (at least, WIP) is f*cked across all the disks (looks like two competing writers went at it) and none of the available tools can deal with it.
It wasn't a super exotic setup either: RAID10 with 4 disks (2 stripes), fairly full and regular snapshots/cleanup, but that's it.
I already converted my root to ext4 because paranoia and I'm probably going to move bulk data (what can be recovered) to ZFS.