Mostly, I like the current sleep algorithm. It identifies phases plausibly, if with some misidentification. But last night it had a much more serious failure that needs rectification.
Last night, I got a few hour sleep before about 3:30, but woke up and thought of some ideas relevant to my work. So I got my Chromebook out and spent perhaps 30 minutes writing them down for latter reference. I then got several hours more sleep, eventually getting up after 10.
Garmin missed ALL of the sleep after 3:26. Presumably the algorithms simply don't allow for sleep that is broken up by a substantial period of activity, so counted 3:26 as the absolute end of my sleep.
I have no doubt that this can be fixed, to avoid missing logging several hours of sleep when it happens