landline calls drop randomly

We've experienced this problem for weeks. Phone calls through the landline drop in the middle --- some happened in a few minutes into the calls, and some took longer.

We've replace the phone set to a different model, and the problem remains. We've also checked this web page https://www.xfinity.com/support/articles/troubleshooting-xfinity-voice, and made sure we follow all the suggestions.

Perhaps we need a new Gateway?