Intermittent Internet Disconnect

Hello, I've been having an Intermittent disconnect of 10-30 seconds every 5-30 minutes for the last 3 weeks. This is occurring in a shared building, and my neighbors with Xfinity are also experiencing this same issue. Modem is a Xfinity XB7 that was swapped in after the issue started but did not resolve the issue. Service tech was on site last week, but the issue has persisted and the tech has not returned. Xfinity's App does not recognize the problem, but the drop is long enough to disrupt work VPN or anything that requires a persistent connection.

What steps can I take to identify where the drop is occurring and then contact Xfinity to return and fix the issue? Thanks.