10 seconds Ping delay and Intermittent Internet Loss

I began to see this problem since last year and had 2 technicians onsite.  1st technician replaced the cable to my home, and 2nd technician cannot find anything wrong. Problem persists. 

My problem is intermittent high ping delay (more than 2 seconds ~ 13 seconds). I don't play games but when the delay is more than 5 seconds to 1.1.1.1, all my Microsoft Team meetings and my daughter's class will get interrupted. 

Here is the monitor graph to IP 1.1.1.1. I have a Linux PC directly connected to Modem and ping 1.1.1.1 every second. Then I put the ping delay into the graph. The normal delay is ~ 20 or 50 ms. And you can see very high Ping delay during last Friday/Monday/Tuesday. Over the weekend it was better. 

https://photos.app.goo.gl/LT7S5NyXDBGuafhP9 

Troubleshooting done:

- Replace Home Wifi Router

- Replace Cable Modem (SB6183 to Netgear CM1100). Above graph is captured when CM1100 used. 

- All the PCs at home have the same problem. It's not a specific PC problem. 

Here is the Modem Upstream/DownStream/Event Log:

https://photos.app.goo.gl/LT7S5NyXDBGuafhP9 

I read some posts here. I want to get some help whether I need to change my Modem again (I heard SB8200 is another recommended Modem to Xfinity). Or it's another capacity issue?

Thanks. Please help. It's really frustrating to the whole family in this WFH period. 

Best Wishes, 

Haofeng