Thanks to VK2AAA's anomaly on 15m WSPR (it showed up at 21.096229Mhz which is outside the expected range of 21.0960 - 21.0962 Mhz range, I now know that this RS-916 has an 120Hz offset on the 15m band.
And again I will need to have to dive into the manuals to find out if I can fix this setting. It's a great little box, but as usual, hardware issues suck.