The error inside the log: Skipping invalid document 'Document'.
The main reason why these documents can be considered as “Invalid” are differences in document definitions: they may have got different field sets and some fields might have different types (like “text”, “number” or “date”).
If you wish to keep documents inside these training batches, you can work around this behavior by following these steps (note that they will change/update the Document Definition in one of the projects):
1. You have to make both document definition's field sets mostly the same in these two projects. It can be done via Update Project feature for any of the projects, but note that the target project's properties will be overwritten with the Source project's properties (including batch types, definitions e.t.c.): https://help.abbyy.com/en-us/flexicapture/12/admin_guide/updateproject/
This way, you will get the same document definition in both of the projects.
2. Publish the Document Definition in the updated project (Target one), and delete empty training batches (if there are any).
3. Depending on which project's batches you wish to transfer, update the Definition for all of the documents in training batches for the Source project and then synchronize them with the Target project.