Excel missing rows

Weird! Just working on an Excel project and noticed unviewable rows. The left edge goes nicely from row 1 to row 733. Then there's a thick-ish green cell-bottom line, and the next row is 1071. Hovering over the green line yields the parallel lines. Click on that and the row number after 733 is now 1070, so 1 row closer. I could do this another 337 times, but wondering what I did to cause this - and maybe how to solve it.

Thanks for any help on this!

Rick