Ok, this was actually affecting all ports/devices for the S8, not what I saw at a first quick glance. I only noticed the port info color changing for this one device at the top of the alphabetically sorted list. But when checking further this is actually the case for all wired devices connected to the S8. All jumping back and forth between presented as connected to the Route10 or Switch S8. The link speed also jumping between 1000 Mbps and 100 Mbps for those actually having a 100 Mbps connection.
I guess this is only related to the presentation (no performance issue), and only in the Alta app.
And I can not say of this has appeared lately as I haven’t used the app much. Also, I just recently plugged in the particular Arris IPTV box that has a 100 Mbps connection which drew attention to this flickering between link speeds (1000 Mbps / green and 100 Mbps / orange).
Edit: Checking in again a few hours later and the flickering changes from down to once every second and up to once every minute.