@Unclwish: i mined the same way as you (Nicehash Heavy on GPU 0, one thread) and it worked for me. Sad i couldn't reproduce the bug. What happens when you add parameter --legacy ?
After adding --legacy miner start to work on one of two GPU. But if remove --legacy no 1st or 2nd GPU didn't work separately. After connecting to nicehash attrib.exe close with application error.
Bug is not for 1st GPU - it happens on any one of two GPU...
Windows 10 x64 latest 19.1.2 drivers. It was on 19.1.1 and on b15,b16 versions too.
Start string is:
jce_cn_gpu_miner%BITS%.exe -o %POOL%:%PORT% -u %WALLET% -p %PASSWORD% %SSL% %* --nicehash --retrydelay 5 --variation 5 --forever -c config1st580Heavy.txt --no-cpu