I have a Pi2 and a Pi4 and also two EW-7811Un adapters. I can install Raspbian on both systems with either EW-7811Un and it will run without issue in that state including using the EW-7811Un. I can install Raspbian and then RaspAp on the Pi4 without the EW-7811Un installed and it works fine.
When i install RaspAp and either one or two EW-7811Un on the Pi2 or one on the Pi4 everything boots and looks fine initially. Over an ethernet connection I can access the RaspAp interface and configure everything as normal, all wlan adapters show and can be configured, the wireless network with the correct details can be seen by other devices however, the second I try and connect to the wireless from another device the Pi stops responding. With a monitor connected the picure freezes, ssh and vnc connections drop, the LED on the EW-7811Un turns off but the wifi remains visable to other devices, they just can't connect to it.