If a customer that has been using the hosted/SaaS solution for a while reports that the the system "can't connect" suddenly - as in they just get the spinning 'connecting' graphic below, it is likely that something has changed in their IT infrastructure.
Thin RDP relies on being able to transmit an HTML canvas to the end user, and it could be running through a proxy or firewall that has been re-configured - some proxies don't support WebSockets, or WebSockets aren't enabled. In these instances, this makes the connection fall back to Ajax which is much slower.
ZScaler and Forcepoint
As an extra point, we have had feedback that the configuration of ZScaler and/or Forcepoint (if they use it) can affect the ability for ThinRDP to connect. We suggest if you are running ZScaler or Forcepoint, that you may need to add the SSL exception for *.myp11d.com or to add app.myp11d.com.