There is an option
pmset networkoversleep
Maybe this is enabled and the devices are trying to share something like airdrop or other shared resource etc... just guessing here though.
I did some more testing today, checking my router logs after I got home from my 45 minute commute. My iPhone connected to my WiFi as expected and my MacBook, sleeping in my backpack, connected about 15 seconds later. It connected again a bit over an hour later. The wifi.log had entries confirming that. The networkoversleep option is off, but I have no sharing services enabled anyway.
I don't have a problem with this behavior personally, but it's a problem for the project, so I'm hoping I can find a way to disable connecting to APs during sleep. I'm surprised how hard it is to find information about exactly what's going on during this.
Console logs at the time of the connection? You should see a few other things happening around the same time.
Can you clarify a bit more about “sending Macs down the wrong authentication path” ? What issues are caused by the laptop hitting the wrong Wi-Fi network? Is there a machine certificate involved? Is there a secondary agent that interacts with the login process? Are users unable to login to their laptops if it accidentally connects to an “other” Wi-Fi network?