I just bought this machine from an eBay seller who builds them for people and it seemed fine at first. (It’s running Mojave.) But twice in the first 24 hours I have had the WiFi get very slow. When I try turning it off and then on again, it will refuse to connect to any access point from then on (telling me it could not be joined and to move closer to the wireless router). Restarting fixes it but obviously I can’t be restarting every 12 hours. Any ideas about this? I could ask for a partial refund if it turns out to be a hardware issue, but what are my other options for WiFi on this machine?