I think I managed to figure this out. One thing I didn't mention in the description is that we have two different RDweb servers behind a load balancer. This issue seemed to come up whenever we would failover to the second web server. Turned out to be related to an ASP.NET MachineKey nuance setting in IIS. Both IIS instances for RDWeb, Feed, FeedLogin, and Pages need to be the same.
Microsoft walkthrough on it here...
https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/rds-rdweb-gateway-ha