Internet Signal to Modem Dropping Every 15 Minutes for the Last Two Months

Our Comcast Business Internet signal has been dropping every 15 minutes for the past two months.  From the logs, the WAN IP address seems to be resetting every time...to its original address.  We’ve replaced the modems twice.  They’re Comcast approved modems.  I’ve tried contacting support and security up to a dozen times, but all I’ve received are non-answers.  What’s going on?  Screenshots from the logs below.