I am using a 75 Mbps broadband connection with my Archer C20 router which at most has 3-4 devices connected simultaneously

However I've noticed that intermittently the speed of my connection drops to 20Mbps and the latency spikes significantly.

At such moments, I'm having to reboot the router which immediately fixes the speed and latency issues.

I've already scheduled the router to auto-reboot every morning at 7 but I'm having to reboot it 2-3 times a day to fix the drop in speed and spike in latency.

Please advise