The only fix found is to fine the old Bluetooth device you own or barrower. Using my oldest iPad for programming the Timer work the best. Programming with my newer iPhone is the reason I have issues.
At this point I would not update any firmware on any timers still working. Out of 5 timers, and I have only 3 truly useable. The other have different issue with program. One won’t delete schedules and other battery reading 40% with new batteries. Yet change to a different program screen the batteries show full charged. All because my iPhone was used to program them.