Key Signature was selected (Eb). Then I get the 3 Natural Signs to UNDO the Key Signature. It won't delete

I selected Eb as my Key Signature (I've used MuseScore for many years). First, I noted that the Key Signature was unnecessarily placed in the middle of a System line, unnecessarily, not by me. I tried clicking on the extra Key Signature and canceling it out by setting it to all Natural Signs. But then I couldn't get rid of the unnecessary Natural Signs. I'm not sure where to go from here. One thing is definite, it's more than a phantom image. The added Key Change is real and truly does affect notes in the measures, beyond it. The file is below. I was in the middle of my notation when it happened.