Hi! Sorry for the lack of answer, i had absolutely no time to come here in the last few weeks.
My problem got solved. Not by myself, though. I tried (almost?) everything on this thread, up to the hard reset, but nothing worked. I contacted one of the team members who is on the forum, and after his intervention, i got an answer from the support. From there it went pretty fast, they changed my phone, and i have a new one, which is fully functionnal, and has been for the past few weeks.
The only comment i’d have is that they changed everything, up to the outer case, which was probably not in question here… but that’s the subject of another thread, i guess ^^
I don’t know exactly where the problem was, in the end…