What is the value you finding ?
If value of valuelist contain finding operator, it can't be find using checkbox.
ex. if checked value is
this means find exactly same as 'a', so the record checked '==a' is not found by the criteria.
Has the field type been recently changed? If the value of the checkbox is a text but it was inadvertently changed to a field type of number,then you may have this issue of not finding what you perceive to be there. Verify that your field definition types are correct and also if the value is "stored" or not under "indexing"
The field is set to a value list value when the box is checked.
The value list value can be found with a checkbox. This has been working without fail for a long time and the checkbox finds work well. I watched the field in the data viewer all through the find process and the value list value looks like it is good at all times.
The field is currently set to None under indexing. I will change that as soon as I can and try again. Nothing has changed about the field. I did not see anywhere about the value being "stored" or not. It is not a calculation value. The field type has not change in a long time, not ever actually.
So far as I can tell right now only this one record is affected. Also this does not have a problem in FM13. The issue seems to be with the FM12 clients. Hopefully the index change will fix this. If not I will let you know.
I suggest you click inside the field in question and have a look at the field's index (command + I or Insert > From Index). That can sometimes show you if there are values in the field that APPEAR to be the same but in fact are subtly different (eg. a leading or trailing space is very hard to spot). If you find that there are variants on the field value you are at least part of the way to resolving the problem. Then you have to work out how such variants got there, especially if the chief data entry method is by checkbox.
Try turning off the indexing for that field, saving the change, and then turning on again.
If that fails, export the whole table to an XML file, delete all the records, and reimport,