Why do not all sites open on the iPad?

Question

iPad

Good afternoon !
There is an iPad 2018, iPad mini and a router (mikrotik, d-link 300, asus n12) in access point mode, with this scheme, sites open every other time (everything works on a laptop and iPhone).
If you configure the router in router mode, then there is no problem, all sites open.
If you configure a proxy on the router in access point mode and register a proxy on the Ipad, then all sites open.
what is the problem i cant understand