Last Seen Syncing

I’ve got many users on my box and for whatever reason, sometimes the sync client has problems sync’ing data; it can be many reasons, like dns not working and it doesn’t really matter…

, but, I’d like to find out how long since they’ve been sync’ing, like a “last seen” list.

Is there nothing like this existing?

The sync client has an activity log with time stamps. The web interface has the same activity log under Apps - Activity.

I don’t understand what you mean?

I have 200 clients; you mean I should log into each and every one of them?

You can use the occ-command to see the last login (can be also for calendar or contacts, it doesn’t have to be the sync-client):
sudo -u www-data php /path/to/nextcloud/occ user:lastseen username

I’m more interested if it can tell me when the last successful sync was done to see if it’s a current sync

The server currently doesn’t know what the clients are syncing and if it was successful. As a user you can decide not to sync certain folders. That’s a new feature -> moved to feature request.