This problem occurs occasionally. The issue isn't that the WiFi is broken but that Apple devices weren't being patient when requesting a DHCP address and giving up before one can be allocated.

Mikrotik by default has a built in pause before delivering an IP address via DHCP. This is to allow for other DHCP potential servers (authoritative) to reply first which helps to stop broadcast storms when accidentally connected to an existing DHCP enabled VLAN. Unfortunately some iOS devices don't wait around and will disconnect before a lease is sent.

By changing the Mikrotik DHCP service to authoritative = yes this delay is removed, addresses are delivered immediately & iOS devices reliably connect to the network.