My SH4 does weird stuff sometimes and becomes unresponsive to pings etc. Nowhere near as bad as yours, I don't have your post RS errors etc, and my D3.1 channel is at 4096QAM, so I've not bothered trying to explain/complain to VM's call centre staff. I'm in modem mode so internet still works, the periods of time it has issues correspond with an increase in pre-RS errors, but nothing else seems impacted.
https://imgur.com/zkQb7kR.png
The loss is only from my server to the SH, it can still get out to the wider internet.