Date field returns error in "Create records for multiple templates"-script

Hello, I already posted in another part of the community, I’m wondering if this section would have been a better place?

The core issue is that a date formatted formula column causes an error when creating new records with the error as below.

ERROR
j: Can't create records: invalid cell value for field 'Date'.
Cell value has invalid format: <root>.0 must be a string, <root>.1 must be a string, <root>.2 must be an object
    at main on line 131

Thanks for your ideas!