@Wilson75 hey,
Sorry for not circling back on this, its fixed it seems
I think the cause was an incorrect battery calibration.
My “issue” since a long time was that my watch would never reach 100%, always stopped charging at 90-ish%, this is because I almost only use a modern multiport charger thats supposedly smart…yet incredibly dumb, because the current draw from the watch passed 90% is so weak the charger refuses to continue supplying it current…and it may have wrecked the battery calibration over time.
I fixed it by using a dumb brick, which finally allowed me to reach 100% and my problems went away !
I’m still debating sending it for a battery replacement since it last so much less than before, I noticed it when going on a 10day bike trip, I forgot my charger so i put it in “endurance mode” with nothing else (and turning off the watch in the night) , yet I barely managed 25 hours of training instead of the 70h advertised.