When it comes to conditional formatting not being applied to all cells, here are some steps you can take to resolve the problem:

1. Check that the range is set correctly – the cell range you are attempting to format may be incorrect, or incorrect cell criteria could be entered.
2. Look for incompatibilities – if array formulas or data validation is enabled, this may cause a conflict with the conditional formatting.
3. Verify the formula syntax – check the formula syntax and make sure that it matches the criteria you are expecting.
4. Check for missing cell references – missing references in the conditional formatting formula may cause cells to be excluded.