Hello Tim,
I had a similar problem for me it had to do with a new security system that was implemented by my company.
I created a ticket at mendix and got some advices to try, although for me the solution was to ask my security provider to open some ports.
I found this out by connecting to a different network and there it was running fine without the issue.
Advices from mendix i got:
- update to mendix 10.6.5 or latest but that is what you already did
- removing all local copies of this project from your machine before downloading it again from the Team Server?
This seems to have cured itself by magic.