Where is the slippage?
 

Have you ever made a stack of blocks - then decided YEARS later you needed a few more - tried making one - thinking you were using the "same" techniques - put the block together - and it's not the same size as the others?

(Fortunately, I only cut and assembled one - now I need to try to figure out how to get the "more" ones to match the rest of them.)

Actually, it's about the 50th block that is "wonky"!

I'm usually quite good at getting things to end up being about the size I'm expecting, so I'm definitely a bit puzzled by this one.

It could be in the cutting - don't remember which ruler I used - or it could be in the needle setting. I'm thinking it's more likely to be in the cutting.

I had that happen when I bought a new square-up ruler between making the blocks. Had to revert back to the old ruler. Now I only buy one brand of rulers for general cutting. It was surprising how much the rulers measurements differ between brands.

Yes, it has happened to me too. I just try my best to get the quilt done. It is so frustrating !!