ARD: 1 iMac is only available on wifi, the other only on LTE hotspot

Hoping someone can help me out with this one. I'm new to ARD but have the system up and running, but am experiencing a weird issue.

I'm using ARD on a 2014 MacBook Air to connect to 2 different late 2013 iMac's in 2 separate locations on 2 totally separate wifi networks. All Mac's

are running 10.10 and ARD 3.8.4

iMac #1 will only connect if I'm using a standard commercial wifi network (ex: coffee shop), iMac #2 will only connect if I'm using my LTE hotspot (Rogers iPhone 6)

I will receive the standard ARD message about checking screen sharing and network configuration if I select the wrong method to connect to a given machine.

I'm literally sitting in the same location, but have to switch the airport connection on how I'm accessing the 'internet' to connect to the proper Mac

Any help would be greatly appreciated

Thanks

Karl