Lookup field not populating from parent table

I have a lookup field from a parent table, where the field auto-populates based on selection in the reference field. However today it stopped working properly. The values are all still in each record, but if I add a new record, the lookup field no longer auto-populates. Also, if I take an existing record and change the reference field value, the lookup field populates with "???", although if I put the reference field value back, the lookup field re-populates with correct value.

I've made no changes to the lookup field or the relationship. I have made other unrelated changes to the child table (which is a join table in a many-to-many relationship). I tried removing the lookup field and adding it back, but it did not fix it. Can anyone help? Thank you!

Parent table = Controls
Parent table reference field = Control ID
Parent table lookup field = Control Description (NOT WORKING)
Child table = Evidences Mapped to Controls




Adding new record:

Existing record:




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Diane Sinawi
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