One or more Pleo expenses have a category that doesn't match the rules for expense accounts in Datev. These expenses fail to be exported.
Categories (reflecting expense accounts in Datev) need to follow the following rules:
They cannot start with 0
They cannot contain spaces (e.g., account "1245 04" should be written as "124504"
The go to the Categories page in Pleo and fix the affected numbers.
Double-check that the category has been updated on the affected Pleo expenses before re-exporting.