Hi Lowell,
The user ppm_invalid_user should be an internal user and not visible in PPM UI, there are couple of things which could be looked.
1. Does admin user has all the global rights permission?
2. Does admin user details has been changed in terms of resource id etc
3. Could be an audit trigger issu
I see you logged a case and regional support team will have a look at it and update you.
Regards
Suman Pramanik