Question marks appearing in custom eText output

Summary:

Custom eText payment format in BI Publisher has question marks inserted into output.

Content (please ensure you mask any confidential information):

I have created a custom eText format in BI Publisher for payments, deployed in the Custom folder. The eText RTF template outputs a fixed-length txt file, and all the records are correct, but one specific record type always has 10 question marks added to the beginning of one specific record type.

Below are screenshots of the output and the relevant section of the eText RTF template:

Has anyone experienced this before with a custom eText format, and is there any known solution?