Okay, obvious suspect is that the new router has a slightly weaker signal. Wyzecams aren’t noted for robust radio strength. Approaches include repointing router antennas, adding an extender, changing channels, running a new AP, etc…
Sigh. Okay, just guessing some more, but maybe the old “5 Ghz has same name as 2.4 Ghz SSID” mesh router thing is confusing it. See if you can separate the names. I would also consider physically resetting the camera (button push and re-register in the app). Sorry I don’t have any other ideas right now.