Honestly, the iFly devices are a giant pain in the neck when you try to use them on multiple networks. It is problematic to get them to do that. To minimize issues, it's best to delete all previously-used networks so that the device only knows the login credentials for a single network at a time. But of course that makes it a pain in the neck to change between networks frequently.
I got to the point where I just never let my 720 log into any network other than my Stratux in the plane, to avoid the issues/hassles associated with using it across multiple networks.
I would guess that if you delete the network you use at your plane/hangar, and then set up the 740 to use your home network, you wil be able to get both the 740 and whatever other device you're sharing with on your same home network, and it will work.
Then, when you go back to the airport, delete your home network and re-login to your hangar/plane's network, and it will probably work again like it always did.
My personal suggestion is to just leave your 740 configured for your plane's ADSB network, and don't try to use it anywhere else. It's just not worth the hassle.