Hi Rob, thanks for supporting here !
The Jam instance is at SAP, as far as I know in Walldorf (Jam12) our Company ID is 3501904P
The issue occurs on any browser.
We know that the root cause is a locked S-user associated with the email adress. If we ask SAP Support, they will tell us "user xy has 4 S-users, one is locked" - if they then unlock this one, we can resend the invite and it works. As far as we have figured out, it seems as if the oldest existing S-user is taken, which explains why it is often locked.
SAP ID Service should retrieve the S-users to an email adress, but skip the locked ones.
Bye, Johannes