This is tough because it might be code/might be something in the environment. Easier if there's a way to duplicate this, for sure, in another environment.
When you plug in the iPad, it does a few things. It says "Hey! I'm charging! I can do stuff now that drains the battery usually, so I wait until I'm charging" So basically, it *might*, as I don't know for sure, but it just might turn on other connections. This will cause it to drop.
Have you tried looking at how/why other things disconnect and weeding that out? Jabra has a great guide with some hints that might apply.
I have an iPhone 6+ and Mini 4 for testing... but before we go that route, do you know of any other ways to duplicate this? Like simulator + reader? Plus, if I need the physical card reader, I'll have to break this into milestones to either buy, or wait for you to ship if you chose me.
BLE on iOS is easy, kinda... there's only a few calls, but you gotta kinda pay attention to where the things are and the surroundings. There's probably something happening that you haven't caught, try using a BLE-reader app to see if any device lists change/update. I'd love to fix this. I can break this up into milestones for finding. I just would dislike to learn it's environmental and can't repro