Cloud Collaboration - Project is full

[daeron80]

"The project is already full. No more contacts can be invited."

Experimenting with Cloud Collaboration in hopes of using it for a colleague's remote recording. I was able to share a couple of sessions between two computers in my office. It was working nicely. Now suddenly, every session I create says the above, even though it hasn't been shared with anyone yet. Using 2018.7 Ultimate/HD Native/Omni on a 2013 Mac Pro running Sierra. Things I've tried:

1. Search DUC
2. Sign out and back in
3. Close project, sign out, close PT, launch PT, sign back in
4. Sign in via the Dashboard instead of the File Menu
5. Clear cache on all projects, delete all projects, restart computer
6. {Edit} Install 2019.5

Looks like one guy got it solved with a Support Case. Another did not, and claims that only the paid cloud works. Both are BS. Sending an invite is a dead simple thing. Shouldn't require special help or $$. Avid just need to fix this insufferably dumb, time-consuming, image damaging problem. Pretty sure my boss is both less confident in my ability to find a good solution, and has a bad taste in his mouth about Pro Tools.