nfc

Yes

Just to be sure, which one do you mean? The 1v92 image from the website?

perhaps my reader does not "finish" the transfer properly and the nfc state machine is left in a undefined state.

It's possible, yes. Although presumably it's doing something different to my reader since I've tested it to death with what I have here.

I don't have a proper contact at Nordic, no. Since you have a build system set up and know your way around the code, I'd suggest you take Nordic's NFC sample code and see if you can reproduce with that - if you can, you/I can just post in the Nordic devzone and see what their reply is.