I think I may have found one explanation for the “multiple derailments on the same day” bug.
I had assumed that you could only derail at the time of your deadline. But apparently if you were in the red yesterday, the system will derail you if you’re in the red at any time during the day.
This causes a problem with any goal that always goes into the red mid-day. One of my goals is always in the red during the day but goes back by my deadline. So if I derailed the previous day I will always derail the next day.
This is very surprising behavior - I would never expect that it could derail me at a time that was not my deadline based on the previous day. Goals should only derail at the deadline.