After further testing, it seems setting a rule to turn ON and additionally setting specific actions for brightness and color temp is what’s borked.
Reviewing rules history (which always says successful even when not successful) one of the secondary actions is firing before the ON action. E.g. the brightness fires prior to ON or the temperature fires prior to ON. I first tried deleting the entire rule and making sure the ON action was first in the list. That didn’t work. I then just deleted the brightness and temperature actions and just left the single action to turn ON and that worked in one test.
Would be interested to know if anyone else with this issue has those actions set and if removing them succeeds in turning the bulb on.