This is something I also ran into last week. It looks like the Gainspan module is driving its TX pin high (idle), even though it's not being used (we use SPI). I've been in contact with Gainspan to figure out what's happening exactly, but so far they have not been able to reproduce the issue on their own modules, so perhaps there is something in our backpack hardware that triggers this.
If you need to get this working now, you could try to cut the trace to RX1 (which connects to the gainspan TX pin) on the backpack, which should work without limiting any functionality (though I haven't tried this myself yet).
I'll keep you updated in this topic if we make progress on this.