Wi-fi on iPhone constantly falls off, MGTS provider, sercomm rv6699 router, what should I do?

Question

iPhone

Tell me, plz, in which direction to dig. On the iphone 11 (although the same problem was on the last 7m), the 5GHz Wi-Fi network constantly falls off, and often it falls off and then is not even in the list of available networks for several minutes. A similar network on a laptop works perfectly and never falls off (including when watching a video, making phone calls, etc.).