Connection drops, no OFDM downstream channel lock

Spent over a week trying to get some help with this issue and feel like all I'm doing is banging my head against a wall. Just over a week ago Comcast came out to upgrade the equipment outside my home because fiber has been installed in my neighborhood. Prior to this appt my Netgear CM1200 worked smoothly, my downstream bonded channels had full service and one OFDM downstream channel locked as well. After the installation was complete, and ever since, my downstream channels now have partial service, and my downstream OFDM channel does not lock. Power levels also dropped drastically on downstream channels.

Called the tech supervisor who came back two days later and he added a second power amp inside the house, but no improvement. Next level crew came two days later. They rewired the power amp to run directly off the new fiber connection behind my house. They ran a new dedicated line from the main splitter inside my house directly to my modem. Downstream power levels were improved by this, but the terrible connectivity issues and the partial downstream bonded channels service, and no OFDM downstream channel lock issues remained.

Supoervisor then sent another tech out a couple of days ago who put another splitter in my attic that lowered my power levels again (still within specs though) and insists nothing is wrong with the line coming into the house or inside the house, must be my modem causing the issues. The modem is not even three months old, and it worked PERFECTLY prior to the fiber "upgrade" install. So what I'm told to believe is in that two hour window during which the first tech performed the install, with my modem not even attached to the line or powered on, it somehow developed an issue that is now the cause of my problem. I'm sorry, but that is an insanely difficult pill to swallow. 

Have spent hours with Netgear tech support walking through all of their troubleshooting and they conclude my modem is working and there is an issue with Comcast, somewhere up the line there is a problem.

So like many before me I'm in the Comcast says it's my modem, and Netgear says it's Comcast purgatory. So the tech supervisor tells me only other way to test is get one of their modems and see if the problems persist. But here's the rub - the 6 year old used piece of garbage Arris TG1682G they gave me is a DOCSIS 3.0 modem! This doesn't test my ACTUAL problem at all, which is their line not locking my OFDM downstream channel and causing horrendous connectivity issues. Of course the garbage modem I was given works, but that's not the point. My Netgear CM1200 is a Comcast approved compatible device. With it and my Netgear AC1900 router I had a STRONG, STABLE connection for EVERY single device in my home. Now, with this Arris POS if more than 3 devices connect to the wifi it starts dropping the signal.

At this point I've been told my only recourse is to go buy another brand new Netgear modem and connect it to see what happens. If I do so, and the issues persist, only then will I get additional investigation into my issues. This is beyond frustrating. I'm NOT a conspiracy guy like many around the web who say Comcast pushes you to use their equipment instead of your own, and a situation like mine where an upgrade in the area happens is a common time it occurs. But it's hard not to stray down that path.

At any rate, if anyone has any ideas or suggestions, I'm SO open to hear them. Thanks for reading.