MOCA 2.0 speeds plummet after installing S33

I got an email from Comcast saying my Netgear CM600 wouldn’t give me the speeds I pay for (800 mbps) so bought an Arris S33.  

My setup is as follows:

I have a 1 GHz 2-way splitter outside my home with a MOCA POE behind it.  One one leg I have an Actiontec ECB6200 MOCA 2.0 bridge connected to an ASUS RT-AC3100 router which is connected to the modem.  On the other leg, I have another 1 GHz 2-way splitter with one leg of that going to a TiVo Roamio and the other a TiVo Bolt.  The bolt is acting as a MOCA bridge.  

With this setup and my Netgear CM600 (Docsis 3.0) modem, speed tests done on the “TiVo” side of the MOCA bridge using both my MacBook Air and Apple TV 4K max out at about 475 mbps and are consistently above 430 mbps on the ATV using the Speedtest app. 

After swapping in the Arris S33 (Docsis 3.1) modem, the speed tests dropped to about 275 mbps.  This was fairly consistent.  I tried replacing the entire setup on the TiVo side with another ECB6200, but the speeds actually dropped to 130 mbps.

The MOCA network is running on what the TiVo reports as channel 15 and the ECB62000 reports as 1150 MHz.  The S33’s OMFD frequency was 957 MHz.  All other channels were below that. I wouldn’t think these would interfere, but they apparently do as when I swapped back to the CM600 my MOCA speeds returned to normal.

Note that my area was updated to multigig speeds recently, but I don’t have that. 

Any idea why my MOCA speeds drop so dramatically with the S33?  Does the Docsis 3.1 (OMFD) frequency used my Comcast interfere with MOCA 2.0?   

Some other oddities that aren’t related to MOCA as far as I can tell.

1. I connected my MacBook Air directly to the S33 with a USB-C to Ethernet adapter and couldn’t get speeds faster than about 133 mbps. Didn’t matter which modem port I used: 1 or 2.5 gbps. This made no sense since I could get faster speeds through my router. 

2. Connecting my MBA directly to the CM600 gave me speeds around 450 mbps.  Again not as fast as through the router, but faster than the S33. 

3. Wi-Fi speeds seemed faster than LAN speeds in general for some reason.