User removed from the site - my account.yaml file looks fine

Recently I went to my site and the instead of the site got the new user creation screen. (I only have one user.) Obviously this was not ideal. I don't know how it happened. I checked grav.log and it only had one line grav.DEBUG: Flex: User index updated, 0 objects (0 added, 0 updated, 1 removed). [] [] for a date/time when I wasn't on the site at all.

I logged on via ftp and my user/accounts/ myaccount.yaml file was still there and matched an old copy. I deleted the yaml file and added it back - still stuck on the new user creation screen. I recreated the account using the same details and it created just fine (no errors about existing users).
I'm running Grav v1.7.0-rc.16
Any ideas on what's going on?
Thanks

Hi

Grav v1.7.0-rc.16 is not stable, it may be the cause
The option "GPM Releases : testing" is activated (Config > system : advanced > GPM Releases)
Return to version stable

Thanks, I'll look into moving to v1.6, I don't have many plugins so hopefully it'll be a smooth transition.