Hi @ptillisch,
in the example accompanying the software serial library in the Arduino UNO R4 core I see written:
// Note any pin can be used for TX, but only the following pins
// can be used for RX:
// D0, D1, D2, D3, D8, D14, D15, A1, A2, A3, A4, A5
... you do not specify D14 (A0), while you do specify D11 and D12, so ... which ones are really usable? 
Guglielmo