on 1 spreadsheet in a multi-sheet file most cells are infested with validity drop-down function.
This includes several data ranges. Copy of an empty cell into an infested one will remove drop-down and data.
Using the brush, tickle empty cell, then move it over the infested data cells will alter content of infested cells, data.
Cut, paste only formula, validity dd remains.
I have already asked similar question before, received no answer from GURUs.
May be I found a way:
What does not work: Ctrl+x, Paste special, only formula. Drop remains.
What seems to work:
CTRL-+x cell or range, paste it Edit paste special, only formulas into empty area of sheet.
Check source area. Mine was now empty of drops.
Ctrl+c from deposit and Paste only formulas into previously cut area. DropDown’s gone.
Unresolved: How cells got infested.
If I don’t come back soon to this post I was successful in removing the DROPs using above method.
I might check later whether the the cause of problem has been discovered.
______Edited - replaced invest with infest
→ 
) to the left of the answer that solves your question.