Spatial Join is deleting fields from the Target feature

Question

I'm trying to exectute a Spatial join between two similar feature classes, which contain data about utility poles. I've done this many many times, and never encountered this issue.

I set up the Spatial Join - delete all the fields from the Join Feature, and specify how I want to join with the existing target fields (basically populating any empty columns for pole age, height, etc.)

As soon as I close the Field Mapping interface - it 'thinks' for a second, then deletes half of the target feature fields. I've checked and all of the fields match type and format. It makes absolutely no sense. Please help.

RoehamptonCable · Answer

The Tables were imported into the project (and default GDB) as a feature classes. Doing so automatically gave them ObjectID fields, which appear to be present and correct.

BSBlagojevic · Answer

Reason for could be Target table - Excel file (missing ObjectID field in table which you are mapping)?!.

RoehamptonCable · Answer

Also - if I try to do a spatial join with the default field mapping (ie. it just adds all valid join fields to the end of the target table) - then it works perfectly! All fields are present and correct. But the second I try to map Target fields to Join Fields - it deletes a whole whack of fields altogether. Its madness.