Conditional formatting stopping mid workbook

Good afternoon

I have a calendar reading from multiple worksheets to display staff worked shifts and absences across a year

I have a number of different conditional formatting rules set up for different absence types, and it has been working fine.

Today I have added a different rule to see if any overtime was worked. My issue is that any dates up to around mid march seem to display fine, but after that the most recent rule does not work.

I have checked that the new rule is applied to all cells.
I have checked that the data formats do not change after a particular date.

Does anyone know if there is effectively a "processing limit" for conditional formatting to work. This is the only thing I can think of, is I have gone past the point where it wants to keep working.

You have checked to see that the data (cell?) FORMAT didnt change, but did you check to see if the format data itself (specifically the dates) changed? I have a feeling you may now be dealing with text dates instead of real dates. Test with =ISNUMBER(cell-ref)

Thanks for the thought FDibbens ... I have checked the date formats using the suggestion you provided, and also used the trusty old multiply everything by 1 in the paste special to ensure they are all the same format. still no joy.

hmm OK can you upload a small sample of your WB?

Hi FDibbens

Trimmed down version attached.

Tab "List of OT hours shows what should be formatted as "Full OT" or "Part OT" in the Calendar.

As you can see, it stops doing this formatting after February 10, despite there being many more entries that match the criteria.
The list of employees is normally around 1000, I just selected some that fit the criteria for testing.

To help:
Cell AD15 on the Calendar is where you select the employee to populate the calendar.
Legend of leave types is on the right of the calendar.
Shift types are the diagonal stripes.

Disregard the second calendar, it is for something different and I removed data to reduce size of the file.

Thanks for your help

Darren

the formula in the conditional format only goes up to row 166

Formula:

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but worked hours goes up to row 957....update the formula to 957 (or higher) it should work

Thank you

Rookie error !!!!! Testing on a smaller sheet and then implementing in a larger one.