Internet has become unresponsive on a daily basis, every afternoon

For the last several weeks (at least 5), our internet connection will become randomly unresponsive for a few minutes at a time.  This has been occuring every afternoon, starting at roughly 2:30 pm EST each day.  This issue will persist through at least 5 pm, when we typically leave the office.  We've done countless modem resets by using the phone robot, which does not remdy the issue.  I've also connected directly to the modem to rule out our internal network infratructure, with no difference in the results.

This has become a major issue for us, as we rely heavily on our internet conneciton for phone calls (no cell service inside our building), and video calls such as Zoom and Skype are nearly impossible due to the constans "stalling".

Modem levels look good, and it does not indicate a loss of internet connection when this issue begins.

We're at a loss, and it's time to call in the experts!  

Help?

-Bob