Is there a setting that may prevent a free-form text custom field from being updated with a CSV import? The field mapping is set up as it should, it uploads without any errors. But it doesn’t update the field. Would love to hear some thoughts on what may be going wrong. TIA

You could uncheck the Run Server SuiteScript and Trigger Workflows box to assure that there is not a workflow/script that is running after the record gets created that is deleting the value.

That did the trick! Thank you @Alex K

cool, if you have access you should review the Scripted Records page for the record you are uploading, you may be turning off some appropriate validation from scripts/workflows as well by removing this preference on your import