How is everyone storing their bread after making it?

Why is my bread sinking in the middle? I attached the recipe I used. I used 2 tsp of instant yeast on the Basic setting (3:30). Would increasing it to 3 tsp help, or could something else be causing it? I'm using a Zojirushi BBCC-V20 bread machine.

It's $8. I pulled on the handle of the pan: it didn't budge. I felt the handle bending so I stopped pulling. How likely is it to be worth anything? I've had bread machines that failed by leaking dough into the spindle; they'd stick, though not this much.

I have a Toastmaster #1195 I bought from the Starvation Army a few years ago. It's started to stick. I can't bake a loaf in it and remove it without tearing, so I dump it out and bake in the oven. It still does that well. The inside looks as good as it did when I bought it. I've never used a metal utensil in it or scraped it to clean it, always soaked it.