I have one entry that is drastically longer than the data that follows, and I
want it to overrun into the adjacent cells. It used to, but now it won't.
I've tried left justification, but it doesn't seem to help.

Any ideas?

Whether you want or don't want it to run over, you can probably accomplish
this by right clicking the cell, column or row and select Format Cells and
under Alighment see if Wrap Text is checked.

Just a thought.