Mikrotik is closing connections and loggin out hotspot user when there is more then approx. 200 -220 users connected
To avoid this, change the following default values.
Web proxy, which has a maximum of 600 "client connections", increase the value to 2,000.
DNS "cache size" by default the value is 2048 KiB, increase it to approx. 6000.
Keep in mind the hardware limits.