Only things I can think of is does your WIFI router have it’s own firewall? If so it could be blocking it because it does not reconize it as a safe device or conection. If this is the case best bet is to look at your router manual to configure the firewall or your ISP.
Other is the WIFI signal from the router. If you live in a crowded area, and everyone has WIFI this can interfere with the signal, distance of router to device, recent update to the router (some update automaticly), etc can all play tricks on your contected devices.
Hopefully this helps.