Known Issue: Disconnected hosts causing FME Server web interface to become unresponsive

Symptom

Navigating to the Engines page of the FME Server Web UI and then trying to navigate elsewhere, the entire FME Server Web UI becomes unresponsive. 

Cause 

This issue can occur if you have an FME Server with distributed engine hosts and the Core host is unable to connect with the Engine host. When you navigate to the Engine host FME Server will try to establish a connection in order for you to manage the Engine count on each host. The FME Server Web UI becomes unresponsive until the connection timeout is reached for each disconnected FME Engine host. This may take several minutes.

Note, only the user or group of users who have accessed the Engines page will encounter this issue. Also, as far as we are aware FME Server deployments that are not configured for HTTPS/SSL will exhibit this issue as web browsers limit the number of connections to HTTP hosts.

Workaround

There are currently two workarounds:

• Use a second web browser or an alternate machine to navigate the FME Server web interface, and avoid the Engines page for several minutes.
• Configure FME Server for HTTPS/SSL to avoid this issue.

If you need to manage your Engine hosts, navigate to the Engines page and then wait until a toast message(s) have appeared indicating the communication error with the offline host(s). Once FME Server has stopped trying to establish a connection you should be able to use this page.  

Resolution

Upgrade to FME Server 2021.0 b21199 or newer.