The source field that is being looked up may be a number field, but the lookup field itself is often an array. Sometimes lookup fields act as arrays and sometimes they do not.
Here are some of the factors that may go into determining if a lookup field acts as an array or not:
- The field type of the field being looked up
- How many linked records there are
- If there is a condition on the lookup field
- If the number of values for the lookup field is constrained
- If there are linked records with empty values for the field being looked up
- How the lookup field is being used (formula, view filter, automations, etc.)
Overall, I find it easier to recognize that it is too difficult to know if a lookup value is an array for a particular record. I will often use a rollup field instead where I can use a function that ensures the value is not an array.
Comparisons of number fields with zero are also problematic. Zero and blank are sometimes evaluated as being the same. (I’m not saying that is right, but I am saying that it is established behavior in Airtable and unlikely to change anytime soon.)
Put the two issues together, and you can get weird situations, as you have discovered.
That said, I agree that automation error messages could be more helpful. I’m not ready to spend credits on AI troubleshooting suggestions, though.