Can you post the conditional format expression?
Is this a real check box format on the field or is it a layout design that simulates a check box format?
WIth check box and radio button formatting, there can be data in a field that doesn't match the current value list and it won't be visible in the field as long as it is formatted with the check boxes or radio buttons. But any additional data in the field might keep your conditional format expression from evaluating correctly.
Formula is Data:Discontinued = "Yes" Text Color.... It is a real checkbox... Value List is "Yes","No"
When I go to the table to look at the data all I see is the checkbox... how would I lookd to see if there is any other day there. I have put the checkbox in the layout.... perhaps it shouldn't be there? Below shows the layout in browse and edit
Change the box format to be 'Edit box', extend it down, and then check what data it shows for the records that don't format correctly. I suspect you will see, as Phil says, other data in there.
If you are only using the 'Yes' option of the check box then you can specify the value list to only have 'Yes' available.
I am guessing that you have set the field to maybe auto-enter 'No' at creation. Then when you tick 'Yes' the field is actually set to 'Yes' and 'No'. As it works sometimes then maybe you started without the auto-entry, and then added it later?
Another way to demonstrate that theory is to change your formula to be PatternCount ( Data:Discontinued ; "Yes" ). Then it will correctly show the format - but that is just to prove the theory, not to fix it correctly.
Rather than patterncount--which can with some data produce a "false positive" result, I prever to use FilterValues to check to see if a given value has been selected in a checkbox formatted field.
Not IsEmpty ( FilterValues ( CheckboxField ; "Yes" ) )
Will return true only if a return separated value, "yes" exists in the checkboxField. (Clicking multiple checkboxes in a field enters each selected value, separated by a return.)