It's possible that gauge is using the old ID system. (so its ID would just be 12). The new system just uses a generic random number because 12 doesn't differentiate between ECM and TCM or other sources of Engine Speed. The gauges are suppose to migrate to the new system but maybe it's not working right.The default tach says 0 rpm. I added a few random gauges and they worked.
Just hold it and release it in the same spot. Then click remove. Then just add a new "Engine Speed" from the ECM. Then it should have the proper ID.