I made soft pretzels before Christmas. I proofed the yeast before I used it, then I baked half a dozen at the time, and they turned out great.

I put the rest in the deep freeze. The two batches I've made on separate occasions since then have not risen properly after thawing. I don't know what happened. I've frozen these pretzels many times before, so I don't think freezing them is the issue.

What went wrong?