No solution but a lot of questions
I love a mystery, particularly when it’s someone else problem (sorry).
My understanding from your post it’s occurring from different sources? You mention Alibaba and and three other apps, or only from alibaba? Does it only do this with that source? So using a FAST app without a VPN works as expected? (or any other source)
I wonder if you have tried without the VPN, it’s unlikely that not using a VPN for an hour or so will get you into any real problem but I leave that to you.
Am I correct in my reading to say you tried with Wi-Fi and wired Ethernet? In the second paragraph you mention it’s been good using Wi-Fi for 45 minutes. But my impressions from the first paragraph seemed to indicate Ethernet or is the laptop only using Ethernet.
My thought process is elimination of anything that can be eliminated, thus the VPN, also whether the streaming source could be the issue.
The Pro has enough storage and memory that it doesn’t seem likely the cache is a factor. If it occured only on Ethernet that might indicate a faulty Ethernet port or cable.
Before you replace the box it would be nice to verify that it isn’t something else as I am sure you are trying to do. Trying with a different box would be great though, a Plus is only 30 bucks… but “only” is relative in meaning. (Also wired Ethernet is a harder option with the Plus.)
This is of no help at all but I had a similar problem with the network interface on Firesticks ( the fix was a simple app that reset the I terface without a reboot), I have a Pro and I have NOT seen a similar problem them.
Sorry if my musing about the problem isn’t much or any help.