I did a dive with my Descent Mk2 (firmware version 8.10) in Multi-Gas mode yesterday and during decompression I suddenly got an alert like this: "CNS toxicity at 150%. End your dive now." That can't be right, there's no way I was over the CNS toxicity limit at that time. We had done about 42 minutes bottom time at an average depth of 145 ft (44 m) on 18/45 trimix, switched to 50% nitrox at 70 ft (21 m) for 4 minute stops every 10 ft (3 m), and then switched to 100% oxygen at 20 ft (6 m) for the final stop. The alert popped up after a few minutes on oxygen.
The FIT File Viewer shows that at timestamp 4/24/2021 11:39:06 AM the "cns_load(percent)" field jumped from 66 up to 150. It had been counting up smoothly until that point but then suddenly jumped. It kept increasing from there until at 11:53:35 AM it reached 226, and then suddenly dropped back down to 23! I'll open a support ticket with Garmin since this seems like a defect. Has anyone else seen similar problems?
Here's a link to the dive activity. I made it public if anyone wants to take a look.