New modem MB6811 issues - SYNC Timing Synchronization failure

Installed new MB6811 two nights ago, upgrading from MB6800 in place for two years (with virtually no problems).  Activated, then a short while later connection failed and resumed.  Happened again, then from logs once again overnight.  Checked logs intermittently yesterday and it continued to fail every couple hours.  Fully reset modem last night and went through reactivation process again, with basically same results.  Kept failing this morning.  Connection logs looked normally compared to examples from similar posts here - all values seemingly within normal range.

My fix this morning was to go down to the basement and remove a splitter and amplifier that Comcast had installed several years ago.  We don't have cable TV anymore, just internet, so I only need the one line up to our modem.  Took the outside line and routed it directly to modem instead of through those.  Modem has seemingly been stable since.  Posting here in case there is anything else I should be doing, or if helpful to anyone else.

Have been running an automated speed test since changes made.  My old modem was pretty consistently maxed around 960Mbps down & 35-40 up when tested.  We have 1200Mbps service, so we were limited by the old modem and other equipment.  In the process of building a new PC with faster LAN, so will be able to check for gigabit+ soon.  With new modem I've noticed wifi speeds are already faster (same router, new one on the way).  Wired speed has been varying - still maxed at peak, but often dropping to 500-700.  Not sure if that still indicates a problem with the router or not.

Pasting current error logs and connection status below.  I didn't think to grab a screenshot of the before values, but they were not significantly different.  I believe downstream power was slightly lower (around 1 instead of the current 3).