Frequent random application pop up on desktop when working or idling

We're running a mix of dedicated Windows 11 Pro and Enterprise (mainly) VMs for user desktops/AVD.

Less than a handful of users noticed random pop up of other running applications eg. MS Word, etc. whilst they are working on their desktops or their desktops are idling.

Has anyone experienced this issue? Any idea what is the possible cause and fix?