One thing Netduma had me try was making a custom rule under QoS that had port 1 - 9999 Open for QoS and uncheck the box that says something about Netduma games sorry I am on my phone and I don’t remember what it’s called 100%
another weird thing to try did you by chance change the led settings from default ? I have had really strange things that have happened when I change from default and do no or just solid colors .
Last thing would be to do a factory reset a couple times in row and not change any settings or anything and see if that works
By any chance the streams that are failing are they 4K ? Do regular hd and Sd work? When I was having problems 4K streams did the same thing you mentioned with same behaviors but my theory on that is the switch I have has a QoS built in that cannot be disabled and as it was passing traffic into the Netduma QoS and was having a weird double QoS effect.
On the Samsung you could try to make a static IP address on the tv then go into the router settings under lan and make a dhcp reservation and see if that helps .