I agree with Wendy, with Sebastian seeing all those lime greens on the 3.5u, fairly recently, I would have taken him up to 3.25u if at all. Especially as ketones were back down in the evening.
The worry is being able to keep him safe by steering when he has got the tummy issues going on.
With all the fast changes in dose from 2 to 3u, you won't have seen the true effect of each increase as the depot didn't have a chance to settle, and you may have needed a cycle or two more at 3u to allow the depot to catch up.
They can just have off cycles if they're not feeling well, and with all that's been going on with his tummy troubles, that seems at least possible.
Looks like he is dropping tonight into low yellows, if he is low yellow or blue in the morning I'd be looking to monitor closely as he may just be giving you advance warning of a pretty active cycle.