Our users aren't being added to the correct groups after the paypal upgrade. I'm not sure what we're missing, it was working initially, but now it is not.
Presumably the upgrades aren't actually being completed - at the users that bought them showing as active in the control panel?
There may be some logs to give more information, though there isn't an interface into the user upgrade log at this time. (It's the xf_user_upgrade_log table.)
You'd need to look at the table via something like phpMyAdmin -- it should have some error messages (assuming that PayPal is calling back to us). If it's empty, then you need to make sure that IPN callbacks are enabled in your PayPal account.
If you're not comfortable looking for the log, I can look at it if you submit FTP details via a ticket.