By default, your VMware ESXi hypervisor is configured to automatically log you out of its "VMware Host Client" web interface after 15 minutes of inactivity.
When learning to use VMware technologies (or in the case of a lab), it can quickly become boring.

1. Encountered problem
2. Disable the inactivity timeout from the VMware ESXi menu
3. Disable the inactivity timeout from the advanced settings of VMware ESXi

1. Encountered problem

After the 15 minute inactivity timeout (default), the "VMware ESXi" login page appears with the "You were logged out due to inactivity" message.

2. Disable the inactivity timeout from the VMware ESXi menu

The easiest way to disable this inactivity timeout on VMware ESXi is to click on your username, then click : Settings -> Application timeout -> Off.

Confirm disabling session expiration by clicking Yes.
Then, refresh the page for this to be taken into account.

Note that the tab must remain open for the session to not expire.

3. Disable the inactivity timeout from the advanced settings of VMware ESXi

The other possibility is to modify the "UserVars.HostClientSessionTimeout" advanced setting of VMware ESXi.
For that, go to "Host -> Manage -> System -> Advanced settings", then type "UserVars.HostClientSessionTimeout" in the search box.
Then, select this advanced setting and click "Change option".

Note : as you can see, the default value for this setting is 900 seconds (15 minutes).
It's moreover this advanced setting which is modified if you use the technique mentioned above.

Enter "0" as the new value and click on : Save.

The "Successfully changed UserVars.HostClientSessionTimeout" message appears.