ID 492025 - The Timeline Viewer stops caching when Hiero/Nuke Studio is minimised or moved to a different virtual desktop/workspace

Problem summary
The Timeline Viewer stops caching when Hiero/Nuke Studio is minimised or moved to a different virtual desktop/workspace.
This even happens if the pause timeline Viewer when the application goes to the background option is disabled.
This doesn't affect the comp Viewer.
This issue seems to only occur on Linux.

Customer reported version
hiero.n/a

Customer reported platform

Steps to reproduce

1) Open Hiero/Nuke Studio

2) In Edit>Preferences>Performance>Caching disable pause timeline Viewer when the application goes to the background and relaunch Hiero/Nuke Studio

3) Import an image sequence and add it to the Timeline

4) Once the Viewer starts caching, make a note of how much has been cached, then minimise Hiero/Nuke Studio, or switch to another virtual desktop.

5) Wait for a few seconds.

6) Restore Hiero/Nuke Studio, the timeline won't have cached any more frames.

Expected behaviour
For the timeline to continue caching when minimised/in a different virtual desktop/workspace

Actual behaviour
The caching pauses, even though the pause caching option has been disabled

Workaround
None

Reproduced by support
This bug has been reproduced in:
Nuke Studio 13.0v5 - CentOS 7
Nuke Studio 12.0v1 - CentOS 7 - previous regression

Unable to reproduce bug in:
Nuke Studio 13.0v5 - Windows 10, macOS Big Sur
Nuke Studio 10.0v1 - CentOS 7

Earliest version tested
Nuke Studio 10.0v1 - the issue has regressed between 12.0v1 and 10.0v1