Is it only that the ID has been changed, or has your whole Syncthing configuration been wiped out?
cert.pem and key.pem are the two files responsible for the ID (see https://docs.syncthing.net/users/config.html) and without them you cannot get your old ID back. If your configuration is intact, yet the ID has still changed, then this would likely mean that something has happened to either of the two files (or both), e.g. due to disk corruption.
Please post some details about how you installed Syncthing as well and how you got the update. That might help finding the cause.
Are you trying to sync anything funky, such as your whole home directory by any chance? Dunno where MacOS puts its configuration files, but trying to sync those could definitely lead to such problems.
It was strange, at the beginning the adresse 8384 was not connecting, another 5 digit number was given (ID changed too). After allowing Syncthing to access my disk (not sure if previously I gave this permission - Syncthing was used at least for three years with no problems) the adresse 8384 restarted to work.
I’m not good enough to try to change anything in the Syncthing config files in order to re establish previous ID … I’ll just resync my file (no it’s not entire disk) again.
Thé idea there was a major problem with the disk itself is a possibility - maybe one of Mac OS X updates messed it completely.
In order to close this topic, I’ve just resynched everything … took me a minute (for 15GB) cause all the links were there, it was only ID that changed.
Didn’t get why it happened but it’s reasonable to think that an update caused it (either syncthing or mac os x)