I've filled the grid and got 7 clashes (none in the top and bottom row).
For the instruction that is spelt by the dropped letters, I agree with post number 10. The first four words make sense but not the last three. I have "down" followed by the same as the 3rd and 4th words.
Is the perpetrator someone simply doing his job?
Finally, I cannot find this 19-letter warning, which I assume ends at the cell in the bottom row next to the bottom right corner.