I’m not a Garageband user but perhaps I can help diagnose this.
I always connect my Roland FP-30 via the square USB output direct to my laptop, you have the same port on the back of your FP-10 here:
Is that the port that you using to connect to your iPad?
As a side note, I’m always sceptical about using USB hubs and I always go for the most direct route of connection possible from keyboard to laptop/computer using this cable:
I’ve never hooked up my Roland to an iPad so it’s difficult to comment on this side but I do see there are cables available for this:
Before buying more hardware/cables, perhaps the issue could be in the settings in Garageband.
First see if plugging in earphones has any effect on the input/output settings
I have Garageband open on my iMac here, and so hopefully you still have the same settings as me on your iPad.
Click Preferences >> Audio Midi - and then you should see these options:
and then when you plug in your earphones, see if the input or output settings change.
Perhaps play with the drop down options and there might be a configuration of input/output that will allow you to hear the piano in your earphones and also record at the same time.
I’m not sure if you are recording in MIDI, or have the capability to record in MIDI on your iPad.
I have just plugged my FP-30 into my iMac via the first cable posted above.
Notice how Garageband has detected the MIDI source:
What do you see here? Is MIDI an option for you? If so, does it show a MIDI device connected when you plug in your FP-10?
I have headphones plugged directly into the FP-30, I can hear the piano through the headphones, and as you can see in the screenshot above, Garageband is recording what I am playing.
Not having an iPad on hand makes it a little trickier to test your exact configuration, but play around with the above recommendations and hopefully we can get to the bottom of this!