I have an old touchscreen lenvo yoga, I use it with gnome and never noticed this. Checked it for this post, and it behaves the same way :) I use the touchscreen only for scrolling webpages, never wanted to touch buttons on the header, I never use it as a tablet, always in laptop mode.

Played a bit and I could reproduce the issue, in multiple apps, but I don’t know when it happens. Also when it stops registering the touches it also stops registering touchpad clicks on the header buttons, so I guess it’s not a touch only issue, I cannot even click on that ellipsis button with the touchpad anymore. Making the app fullscreen solves it sometimes, also opening the activities overview helped sometimes.

It seems totally random when it happens.