Throttled? or an issue with Cox internet somewhere?

  This has been happening off and on.  I thought it was resolved, but it has reared it's ugly head again.  My upload speeds are dropping fairly regularly now.  They have been unstable for almost 72 hours now, when usually it is only a few hours.

   I have tried Speedtests (via Speedtest.net).

1) when selecting the local Cox server, I get the results I expect  ( I have Internet 100, so 100 down, 10 up), Ping 10 or less.

However....

2) When selecting ANY other Local server, or an out-of-town/out-of-state server, the ping jumps to 30-50, download speed stays pretty normal, but Upload speed drops to between 2 to 5 Mbs.  Again, download is relatively unaffected.  It is ALWAYS the upload speed that suffers.

  This issue used to occur regularly, 3 to 5 times a week.  Starting roughly around 10pm CST (give or take 15 minutes), and last anywhere from 5 minutes to 2 hours.  And I do mean regularly.  I live-stream to Twitch, so I would warn my viewers every night that the stream might ** out around that time.  It was a regular occurrence.

The issue appeared to resolve however, and I did not have issues for about 2 months.  Now the above issue is occurring.   Note, that NO other local streamers (and I have discussed this with 6-8 of them)  have this issue (and they all use Cox as well because it's the only cable internet locally).

It has been speculated that it may be a temperature issue, since it does seem to happen with temps above 85, and temps below 40.  I do live in an older neighborhood with above ground lines. And we have speculated the the insulation on the cables outside may be wearing thin.

I have several friends who work in IT related jobs, and they have been over to help me diagnose.  We are absolutely positive it is NOT my system, and pretty positive it is not the modem or router.  Consensus is that the issue lies outside with the cables, or somewhere between the cable box on the outside of the house and the Cox nodes/servers.

Looking for any insights anyone may have.  Due to my work schedule, it is going to be at least a week or more before I can try to schedule a tech visit.  The low upload speed will prevent me from live-streaming until it returns to near normal.