The only difference I can think of is that they all have older computers, and mine is just a couple months old.
I don't think that it's a problem of your computer because the MKR1000 usually connects to the WiFi router and not to the computer directly. In most cases it's because the WiFi spectrum is very crowded and the built-in antenna of the MKR1000 isn't powerful enough to get a reliable WiFi connection.