For anyone using the willcode/gr-osmosdr sdrplay2 branch, the SDRplay API/SDK version 2.13 is now required. Previously, any 2.X version would work.
There was a change to a function signature in 2.13, and since there aren't a lot of users of this branch, I decided not to sprinkle ifdefs around the code.
Thanks to krippendorf for the fix.