Amazon FireStick loses connection after installation of new modem

My old modem was replaced when my network speed dropped from 150 megabit to 15. With the new modem I'm getting 350 at peak. However, my Amazon firestick, which is located about 18 inches from the new modem, frequently loses connection. On my old modem I had enabled its use as an xfinitywifi hotspot and that setting was copied to the new.  What appears to be happening is when the signal fails is the network defaults to the xfinitywifi network. I logged in using that and so far so good. Any ideas what's happening?