I'm very tempted to spend a few hours seeing if I can reliably repro this issue from the save just before the fight where it happened. Might be hard to do given that RNG is involved though!
At that point it's starting to feel like we're doing the devs' job for them though. The silence on this has been poor. I've had better experiences reporting bugs in free open source projects maintained by people as a hobby than this.
Lots of effort from the player community has gone into tracking down the cause of this bug, reporting it in detail, and supporting people with workarounds - an acknowledgement, a thank you, and a "we're working on it" would be nice.