Right, I’m on (the non-HWE) 6.8 series:
Linux saegusa 6.8.0-90-generic #91-Ubuntu SMP PREEMPT_DYNAMIC Tue Nov 18 14:14:30 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
According to /var/log/apt/history.log*, I installed it freshly back in December (2025-12-12), and journalctl shows I’d rebooted the next day (the 13th), so have been running it ever since.
Since this is so rare an occurrence on my system, hopefully @anonymousdormouse has the ability to try older/newer kernels with their easily repeatable trigger.