blue row numbers in excel
 

I have blue row numbers and hidden rows. I have read that it is due to
grouping but I don't see any signs of grouping. There are no numbers or
anything at the top. I can manually resize the hidden rows but not by the
format menu. I can't unhide the rows by right click or the menu. Can anyone
help me?
Also, when I manually resize the rows and save it then close it and go back
to it the rows are hid again.