Arris SB8200 Crash/Freeze Problems

Comcast: 1.New copper from house to pole. 2.Modem power/SNR in up/down channels w/in spec. 3. Asus RT-AX-3000 always OK when router rebooted; router never needs rebooting. Problem: 1. When Comcast goes down (say for > 5 min) and comes back, modem shows all green + 1 blue light DURING outage and AFTER outage, yet is actually frozen and requires power-cycle to restore. 2. When I or Comcast send modem restart signal (call-in or use Comcast app), modem fails to respond. QUESTIONS: 1. How to determine if it's the modem or the Comcast? 2. ALSO: Today I was able to get the router to crash and freeze while running Zoom and Speedtest (from the Asus router interface). 3. SB8100 is DOCCIS 3.1. Comcast is using 3.1 modulation on the downstream channels (QAM256) and SC-QAM on upstream. (48 channels down; 5 up). Downstream consistently @ 500 gBits+ (sometimes as high as 700). Any ideas?