Internet dropping out, loosing wifi voice connection

First. Please try starting here if you wish;

https://forums.xfinity.com/conversations/your-home-network/connection-troubleshooting-tips/602da777c5375f08cdea3db9 

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Ping statistics for 2600:1408:a:18a::1b62:
    Packets: Sent = 94, Received = 94, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 17ms, Maximum = 794ms, Average = 41ms

That's borderline to out of spec. Please post the entire upstream channels table and the downstream channels table as well. Copy the entire tables and paste them into your next post.

In an effort to try to obtain better connectivity / more wiggle room, check to see if there are any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/reconfigured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage from Home Depot, Target, Wal-Mart, etc. Splitters should be swapped with known to be good / new ones to test.

Also, check the coax cable for any damage such as cuts, nicks, abrasions, kinks, sharp bends, or animal chews.

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Good luck with it !

I have replaced main run to xfinity modem/router with RELIAGINT 50ft RG6 factory terminated coax using a TKCHAX 10-2602MHz, RG6 Compatible splitter at the incoming coax. Are these brands acceptable?