The problem is that the yellow line that shows the number of bars in the area I'm editing collapses and I can no longer edit. I don't know how to stretch the bar out again so that I can work.
Ok, going all the way around, clicking every button, I found that clicking "optimize view" again expanded the bar to cover the entire recording. Will that work every time? I dunno.
It doesn't happen very often. Usually, if double-clicking on the yellow bar, even if very small, doesn't work, F4 works. Another trick is to click on the double-headed arrow at the right below the arranger to put your project to fit the timeline.