I eventually found what was wrong, and that’s so stupid that I can only blame myself for it.
Actually, my service was launched using /usr/bin/fxcored.
However, when upgrading fxcored, the binary was installed in ~/go/bin and not /usr/bin.
Thus, I was endlessly trying to run my testnet node on the wrong version !!
I’m really sorry for this issue which wasn’t one.
Thanks again for your help.
Regards/
@FrenchXCore