Why is my 2018 Mac mini connection slowing down every few minutes?

Hello,
I’ve been playing league of legends and every few minutes, the MS would go up to 150 then a few seconds go back down. (Using WiFi, not Ethernet.) I then did some speed tests and got different results every time. Sometimes great results sometimes bad results. I did the wireless diagnostics and it said “LAN Connectivity Failure, try restarting your router.” So I did that and ran the tests again and It still said lan connectivity failure. Is there any way to fix it? This is my 3rd Mac mini and each of them have all had issues from not waking up properly in sleep and now this one that randomly slows down connection speed every few minutes......