Why can't I filter a board by a lookup field ("No matching results found")?

Short answer: You can't filter a board directly on a lookup field. Add a text field that copies the lookup value with a formula, and filter on that text field.

Why it happens

• A lookup can hold several values, such as a project code and a manager, so the filter can't tell which one to compare.

How to fix it

1. Edit the board form and add a Text field.
2. Give it a formula that reads the lookup column, for example Project_Lookup.Project_Code. It fills when a value is picked.
3. Save and publish the form.
4. Create or edit a board view, and under FILTER add an advanced filter condition on the new text field.

See creating and using board views.