First the environment.
Inside and outside domain match, mydomain.org
All servers are 2012R2, 3 RDSH servers running a single collection of remote desktops (no remote apps), 2 RD Broker servers in HA, 1 RD Gateway/Web access server
External name of the gateway server is remote.mydomain.org, which the SSL matches. Internal name is rdgwy01.mydomain.org. RDSH servers are rdsh01/03.mydomain.org. Brokers are rdbroker01/02.mydomain.org. Internal DNS has the name rdsh.mydomain.org as an A record for the IP's of each of the 3 rdsh servers. The Gateway server has a Local Computer Group for rdsh01/03.mydomain.org and rdsh.mydomain.org
The system worked great for many months, then suddenly, several users are randomly getting "Your computer can't connect to the remote computer because the Remote Desktop Gateway server is temporarily unavailable. Try reconnecting later or contact your network administrator for assistance". According to another admin, this issue started after a batch of windows updates months ago. I have personally never seen the error happen to me, nor has he. But we do have screenshots of it happening to others. Not really sure how to fix it because of this. When it happens to others, they are typically thousands of miles from us :). They complained about getting kicked out repeatedly as well. We didn't have that issue either. We'd take their accounts and use them on night shift all night for general purposes (writing reports, playing 10 hour youtube videos ect) and never have an issue. This has happened on both their home computers (which is the main purpose for the remote system) and with their company provided, domain joined computes taken off premises. This issue *has not* affected anyone inside the premises on the corporate network (there's about 200 systems that use it all day).