Nope. The ticket (
36098) is still open but there seems to be no urgency to fix it. I assume this means that it's not a common problem but that there is something very particular about how I have things configured that is triggering the crashes.
I've worked around it mostly by staggering backups throughout the night. They fail with the crash about 25% of the time now, so I usually have a backup that's at most 2 days old. It's less than ideal, but I use this for home stuff so the only person I have to answer to is my wife if it all goes wrong :)
As a side note, I attempted to go to 11.2 to see how I fared, but the upgrade was a disaster - I had a mixture of the FreeBSD bootloader failing to work and a motherboard failure - this had me massively confused for a while until I realised the hardware was dying. After rebuilding my system back on 11.1-U7 from backup and, for some reason, having to recover all my data from snapshots (thank you past-me for setting up an amazing snapshot schedule!), I was still faced with exactly the same issue.
Sorry I can't be of more help.