I cannot edit users through the user manager. When I try to open one, I get a 500 error. Is that related to this component? I've set up different subscription levels and when a user subscribes they are supposed to be assigned to a particular Joomla user group. That works, but when I change them to a different subscription level through Membership Pro, they are still in the same Joomla group. How can I ensure that when their membership is upgraded, they are given the new permissions?
As this is handled by Joomla core, it's not related to Membership Pro
I would suggest you to solve this error with user manager first, then check Membership Pro again. You can submit a support ticket sending me super admin account of the site. I will try to do a quick check to see why error happens with user manage and guide you to correct it