I have had this issue so far with conditional formatting and OFFSET formulae.
works fine where applied in the spreadsheet but stubbornly refuses to apply in random cells.
the only solution is to delete the entire row or column and insert a new one in its place, copy/paste the relevant data and the formula works!
If I have copied a sheet in order to use as a template for another version, the same cell in the copies has the problem.
i have spoken to a colleague who has found similar issues in his own work with different conditional formulae.
Does anyone else have experience of this?