Hi
Does the field connected to this look up column exceed List View Threshold 5000?
If the field connected to the look up column exceeds 5000 items, the filter on the lookup column will fail and no value will be returned.
If this fits your situation, I suggest that you modify the view of the field connected to the look up column to control it within 5000.
If this does not suit your situation, please provide some screenshots and data samples.
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