Hey, so had a look into this with the team and unfortunately there isn't any bug going on there has just been a mix up with how you expected founders status to function.
So basically founder status is just the signifier that nobody has left the group, and because you have had an account join the team and then leave it has turned off founder status for the group and isn't applying it to any new characters who join.
The members who are in the group before that account left have individual founder status to signify they are part of the original group but as there has been someone who joined and left the group (regardless of why they did this) the groups founder status has been broken.