Newly intermittent internet service

I have a self-owned MB8600 modem which I've used largely without problem for the last 7 years.  Starting since Thursday, I've been having intermittent periods of severe packet loss (between 50% and 99% loss), followed by periods where I have perfect performance.  About 1 time in 4 power cycling the modem resolves the issue, although usually it resolves itself after between 1 and 5 hours.  I have a capture of my signal levels from March of 2024, and the signal levels now are notably worse, although they report the same whether I'm in the state where I have full performance vs when I have 99% packet loss.  In March the rx power was between -7 and -12 dBmV whereas now it is between -15 and -29 dBmV (I can share the full tables for rx and tx if you care).

Approximately a week ago a tech came out to work on my neighbor's cable (this is a 2 unit condo), and changed some wiring including switching their connection from our splitter to actually use their splitter, although I think that was the extent of the changes to our wiring.  I don't see anything physically wrong with our wiring, but something clearly seems off.

I think you'll probably want me to DM with details, but I apparently cannot do so until I have a public post, which this is.  Thanks!