It appears that two things were happening in my case:
1. I’d always been told that a double reset was punch the reset, wait a couple seconds and punch again. Waiting for the display to come up, a helpful member instructed, was a much longer pause, and definitely reset the AST readout. Thank you!

2.Then we discovered that the new oil was apparently slightly different viscosity and we had to adjust up level to avoid a periodic stall out as it approached the top floor - causing the AST, no doubt.

The float in the tank is now set correctly, too, not sure if that was a big deal or not, but unit is back to running.