Diagonal lines across large spreadsheet

[PatriSmith]

Hi. I have abspreadsheet with approx 5000 rows and 10 columns. A few months ago it started showing diagonals lines in random places over the data. It was a 2013 sheet. I copied the data and saved it as a later version. The diagonal lines still appear. I read somewhere a few weeks ago before saving it as a recent version, that i could select all objects and delete. I did this before resaving to the later version. Sometimes lines appear, sometimes they dont. It is not always in the same places. They are not lines of the same size. Do you know how i can prevent these lines from appearing? The data is words and numbers. No symbols, no currency, no decimals. Sometimes dates with slashes.
Thank you for your help.

 

[jasonb75]

Could you post a screen capture showing these lines to assist in identifying them?