network issue

From last month onwards, we had a strange network problem in our building (both). Because of this problem, most of our tenants and we could not connect to our WiFi router. Anytime we connect, it keeps on disconnecting. We never had an issue with a wired connection. This only happens on our sub-router, which we placed in our tenant’s house (in Access Point mode). In the main router, we never had any such issue....