Intermittent loss of upload speeds

Hello.  We have had comcast internet at our home for about 3 years now.  The first 2ish years or so were almost perfect, minus one bad router situation that was quickly resolved.  However, for the last 13 months and counting, we have been having bad intermittent issues.  The primary problem is that Upload and sometimes Download speeds of the entire home drop to 0 or to extremely low numbers, or fluctuate very quickly in which we can easily get kicked out of work meetings, etc.  The issues can last for a few seconds or up to two hours, though most typically 5-20 minutes.  On average this happens every day or two, sometimes multiple times per day.  Sometimes things are just slow, other times we do not have any internet connection at all for the duration.

We normally have 900 download speed and 40 upload.  When the issue is happening and it is "bad," but not so bad that I can't even hit the speedtest site, I can see anywhere on the range from 0 - 900 down, to 0 - 40 up.  Most typically, the download is "fine" like 500-900, and the upload is the biggest culprit sometimes clocking 0.10 and such numbers.  For many months now I have been paying for Net Monitor tools that catch the issue most of the time as well.

We have had comcast techs out about a dozen times.  We have had 3 new modems, a new line to the house, switched to a different pin/connector on the comcast source in the yard (unsure of what that is called), new line into the house, new cable line to the modem, changed splitters, and this occurs on all sources wired and wireless (2 wired computers, phones on wifi, etc).  For the more complex steps that have been done, maintenance has "found network issues" and resolved them several times which did not help our issue, they have "found loose coupling at an amplifier, and replaced the tap feeder pin" which was supposed to possible help but it did not, they showed that the connection was too hot and pulled were able to pull the values from 16 down to 7 or so (expected numbers between -9 [negative nine] and 9 [positive nine]) which they said might have been overloading the modem or similar, tightened everything multiple times, and recently they even finished a more area-wide "network upgrade" that I was praying might resolve the issue.

There has been no real change, however, despite all of this.  The only slightly positive thing is that there have been about 4 periods of time where we got about 2 weeks, one time 4 weeks, without seeing the issue a single time, but it always resurfaces eventually back to about daily, sometimes multiple times per day.  At least once these periods of "no issue" followed an area-wide outage for network maintenance... not sure if they are resetting something and over time it starts acting up again, or if that is just a strong coincidence.  As mentioned I have had about a dozen techs out, though some repeated; I was referred to a manager as we were considered a chronic issue, but eventually that manager began blatantly ignoring my messages and calls after multiple failures at resolution; one of the most recent techs essentially told me that it would be better for us and for them if we gave up and switched providers; and getting anyone else to come out now is a hassle... comcast diagnostics on their side almost never show an outage (the signal remains, though the upload speed hits zero) so they just cancel appointments on me, or say they will charge extra money to come out.  As frustrating as this has been, I am not looking to switch providers, as outside of this one issue, I've been with comcast for many years (different homes included) and they have been reliable.

We are turning to the forums in hopes that somehow this has been seen before by different teams or different customers that managed to get it resolved.  Thanks for any insight or assistance.