A lot of disconnects on a regular basis

I get this message, "Started Unicast Maintenance Ranging - No Response received - T3 time-out;" A LOT. followed by, " SYNC Timing Synchronization failure - Failed to acquire FEC framing;"

I've been getting pages and pages of those since I moved in my house two years and always wrote it off the modem/router until I did some research here. It used to go down several times a day for a few minutes at a time. VERY frustrating.

I realized the tech who installed my internet two years ago used cheap splitters. Since I only have internet with xifinity now, i discovered where the splitters can be taken away. i seem to have a direct line from the outside almost straight to my modem/router [netgear model c7000 v2]. since i removed the splitters, i have been getting those errors less, but still get enough of them to be disruptive. 

I work from home and rely on my internet connection.  For as many times as it goes down, it is entirely unacceptable. 

I've run through all the basic checks from this page and still get pages of these errors...along with a lot of other critical errors such as, " Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4"

While it works, it works fantastically! I get solid low pings and more speed than my plan [300 and tag 350+/- from xfinity speed test hard wired].

what else can the issue possibly be if it isn't poor quality splitters that were being used unbeknownst to me as installed by the tech?