Calculated column occasionally giving #NAME? error

I have a large SharePoint list which contains a calculated column. This column creates a unique ID with the use of a pairing function based on two other columns. This works great, but sometimes (as you can see below), the column gets a #NAME? error instead of calculating the value.

The two columns being used for the calculation are "Grower Number" and "Audit Date". As you can see, the calculation works fine for all other values, even the ones with matching grower number and audit date to the problematic one.

What's going wrong here?