Entity Unavailable- how to?

I am having problem to solve a entity unavailable issue. before going specific, what would be the best practices to deal with this sort of problems, what/where to look at ?

in details:
RPI4 107.4 - 2 sonoff basic with tasmota 7.12 (Boiler & LivingRoom_Light)
after a storm power cut I have to reset the sonoff/tasmota (LivingRoom_Light) back on the home network.
home assistant also have been updated in the middle (104->107)

Home Assitant dicovered it but in unavaible state. With Developer tools /Mqtt I am able to switch it on/off , so not a MQTT issue (set option 19 1 done).
I try to compare with Boiler which always worked fine for a difference, but couldn’t find a clue there.
I try to force the state into developpers tool it doesn’t work, after a little while it revert to unvailable on it’s own.
I disconnect it from the main, delete the entity, and plug it back, it is autodicovered and up again as “unavailable”.
can’t see anything wrong in the log
I don’t know what to do next …

any idea ? (push up)

Did you ever find an answer to this? I’m struggling with a discovery issue where after i add a new device, change the name to something less cryptic, rediscover in HA, names are all good but entities show unavailable. Seems similar.