CustomField mapping problems

Hello,

we have a problem with the synchronization between two custom fields from the remote instance to our local. One field is a single line text field, the other a select list (single choice). In both instances, the value of the remote fields aren’t synchronized to our local issues or more specifically are only returning “null” values (when trying to print the value to the log).

The problem of not receiving the value of a specific custom field also appears in another connection with the same custom text field on the remote side. As this other project resides in our Jira Software instance, I attached the support zip from this one.
The fields we are trying to sync are named as followed:

Local:
.) Name: Kundenreferenz
.) ID: 12820

Remote:
.) Name: Kundenreferenz
.) ID: 10087

Thanks