### **Environment**:

Your OpenProject Version: 12.0.1

### **Steps to reproduce:**

1. Create a work package custom field, tick 'Used as a filter'

2. Create a work package query using this custom field as a filter

3. Edit the custom field and uncheck 'Used as a filter'

4. Open the work package query and try to export as, say, XLS


### **Actual Behavior**

A red error message with "Bad request."

### **Expected Behavior**

The export should let the user know this is due to the Begin of the insertionno longer availableEnd of the insertion Begin of the deletion disabled customEnd of the deletion field Begin of the insertionin filter query.
End of the insertion Begin of the deletion

**Discussion**

End of the deletion The filter Begin of the insertionfieldEnd of the insertion is Begin of the insertiondisplayed withEnd of the insertion Begin of the deletion not actually shown or used in the UI as expected.
But it's still in the query which then breaks whenEnd of the deletion a Begin of the insertionread warning string and the optionEnd of the insertion Begin of the deletion work package export is attempted.

Unchecking 'Used as a filter'End of the deletion for Begin of the insertiontheEnd of the insertion Begin of the deletion a custom field should warn aEnd of the deletion user Begin of the insertionto removeEnd of the insertion Begin of the deletion if there are queries usingEnd of the deletion it Begin of the deletion as such. Or,  the filter should be removedEnd of the deletion from Begin of the insertiontheir filters
On saving/"saving as"End of the insertion Begin of the deletion queries

The "bad request" response ofEnd of the deletion the Begin of the insertionquery, the invalid filter fieldEnd of the insertion Begin of the deletion requestEnd of the deletion is Begin of the insertionremoved (instead of crashing angular)

<br>End of the insertion Begin of the deletion &quot;cf N doesn&#39;t exist&quot;.End of the deletion