Gigablast service, works after modem reset but ~daily gets capped to 10Mbps

I recently noticed frequent (daily) drops in my internet speed and now that I've been paying attention, I want to share the symptoms and get suggestions on what may be the best solution.

It started roughly 2 months ago.  I had been getting pretty solid speed with the following network setup:  Arris SB8200 with Amplifi HD and a single mesh point.  My speed tests run via speedtest.net to the nearest Cox location would return in the neighborhood of 700Mbps down and 10Mbps up.  Switching to other servers on Speedtest would normally drop the down speed but sometimes give me in the neighborhood of ~30Mbps up.  Then when it started, I'd see a limit of 10Mbps up and down regardless of speedtest location.  When I try to login to the SB8200 internal page, it wouldn't open.  After resetting the modem (either by power off/on or via Cox account website) I could then again log in and speeds would be restored.  On the cable modem's event log I would see logged events like "SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=. . ."..  At first it was occasional but it has become daily or more frequent.  About 1 month ago, I switched the router to an Amplifi Alien and the symptoms have continued, except now after a reset I get 900+ Mbps download speed, until whatever is causing the issue happens and it once again drops to 10.

In the modem's internal page, the power levels are mostly 4-7dBmV with exception of Channel 159 which is showing ~10-12 dBmV.  All the SNRs are pretty solid (41-43dB).  The only other weird thing is the very high corrected count for channel 159 (hits over 10million after just a few minutes) but I've read it's normal to have a high count here.  However I wonder if mine is higher than normal and along with the higher power level on that channel, is something wrong there?  There are 0 correcteds on other channels and 0 uncorrectables on any channel.