Which modem do you have and how long have you had it for?Exactly bro. Also, I am noticing when my system is OFF and while LAN is not active via PC, WiFi works absolutely flawless. That's strange.
Like from this morning till 3PM WiFi was disconnecting after every half-an-hour. However, at the time I am writing it's smooth and nothing is breaking the signals.
It could be settings which interrupting time to time. Well, i don't know.
PTCL ones tend to act up if repeatedly powered on and off (by loadshedding).
Get a new Zyxel modem if possible from your Exchange. The new firmware is quite nice and the modem will probably work better than older ones as well.
Sent from my SM-G935F