I have a Brother printer which I've been using the Hotspot with my S7 to print from my computer and working great. Added my MiFi 7730L and it won't print any longer. Why? The printer connects to the jetpack and prints a success page, but the jetpack doesn't show it as a connected device and I'm unable to ping or connect in the network. When I switch back to my mobile hotspot it works and prints as it should. I was under the impression these were using the same build and should work pretty much the same as eachother. Can't understand why my phone would work find but the jetpack does not.
When you switch the network connection from the mobile hotspot to the Jetpack the IP Address of the printer is changing. You need to uninstall and reinstall on your S7 after you hook up the printer to the Jetpack. Check the new IP Address of the printer when it is connected to the Jetpack, not the old one.
IF you are positive you are checking the correct IP Address of the printer while connected to the Jetpack then the next possible issue is a feature commonly called "Wireless Isolation". This feature limits all connected devices to access the internet only and doesn't allow them to talk to other devices on the Jetpack. You can search the User Guide of your Jetpack to see if it supports this feature and disable it to work around the problem.
See page 62 of the User Guide for the Guest Network feature: