I found it. Right smack dab in the middle. I skipped a sequence of threading two heddles.
I thought I double checked all the threading but I think what happened was I checked each half and just didn’t see the skip.
So if you have a skip like that, what is the better way to “fix”? Finish this mat, cut it off and rethread. Or, finish this mat, and then stick in two heddles, thread them, and hang the surplus off the back.
Or, as it was not immediately obvious to Peg, just keep weaving and let it be part of the pattern? At least it is in the middle and not off to one side!
Onward with this mat, anyway.