im not technically new to the site i used the google login before but thats not the important thing, the thing is after all those years i finally tried to pm someone and i got an error saying that the member i tried to pm can't be found, i hope you can help

Google login plugin wasn't updated for the new version of SMF, and the plugin kept emailing Kureha saying that we were running way too many logins for the free tier and wanted Kureha to pay out the wahzoo.

As for PMs, it should work, unless the user account has been deleted, or in some cases there were some old accounts that had a different display name than the username or had odd characters...