Hi there,
the fact that you cannot ssh as a normal (Yunohost) user by default is sort of a feature. If you want to allow users to connect through ssh, you can use for instance the small script I wrote here. You’ll need the LDAP admin (=Yunohost admin) password to do that.
The admin password is pretty stange though, I don’t see any reason it would spontaneously change.
Can you still login as root somehow though ? If so, you can try to change the LDAP/Yunohost password (see here).