Well...I went to the store, the owner and I reviewed the rulers, the rotary cutter - she took it all apart and checked it, the mat (she washed it and checked it thoroughly), the flannel quilt that started all the trouble, the raw flannel yardage I was using to make the flannel quilt...all of the above was totally fine, no problems that she could find.
HOWEVER...we found bird seed wedged in the flannel, and she thinks this is the culprit. I raise exotic finches, I have numerous large aviaries in my house and I wash towels from the floors of the aviaries in my washing machine. Seeds are often stuck in the washer and what must be happening is that when I prewash the flannel, the seeds are wedging in it. This doesn't happen with regular cotton, but this is my first time using flannel.
I bought a new cutter just to be safe, but the shop owner said my mat and cutter were totally fine. She agreed that all my blades are nicked and then we found the seeds...
So, I am afraid this won't help many other people, but for what it's worth...
The good news is the flannel quilt got lots of praise and I am loving it in the winter by the fire. Most expensive flannel quilt of all time, but at least it's a really nice quilt
Lainey