1. Are the Portal Fences linked to networked drives
No, everything is on a local drive (SSD)
2. Looking at your video there was only one flickering Fence. Is the problem only from this Fence or it happened on all fences randomly?
I've not created many portal fences, but from what I can see up until now, is it is not random. It's usually when the portal fence contains several folders/documents when the flickering occurs. Non-portal fences are fine - I've not encountered any flickering with them so far.
When I say "flicker" - it could be that the portal fence is being refreshed several times.
It's not a deal breaker, but it does take away from the smoothness and feel of the UI.
As a interim workaround I've change the fence portal layout/view from "details", to "list"