History job getting full, and stopping the content matrix.
The Content Matrix job history file is getting full and is stopping the migrations from moving further.
The Content Matrix job history.lst file (which is a SQL CE database) has a size limit of 4GB.
When it reaches that size limit (4GB), it becomes corrupt and unusable.
This should not stop the migrations. However, it will APPEAR as if nothing is copying or being logged, since there is no longer a valid job history file for Content Matrix to write information to.
Once migrations jobs are complete, close down Content Matrix, and delete that job history file.
Then, when re-open Content Matrix, a new job history file will be automatically created.
If large migrations are being planned, recommendation is to move the job history logging to a full SQL Server (If possible), to avoid this file size limitation. Otherwise the same problem will eventually occur.
Reference to KB article with a short embedded video on how to set that up (As indicated in step 3).