Symptoms and findings
In the event log event id 12291 from SQLISPackage100 is recorded, together with event id 208 from the MSSQL Agent service:
In the MSSQL log for the job, the following error is recorded:
The package execution returned DTSER_FAILURE (1).
Resolution
This was caused by some of the job tasks not having their database selections stored properly:
So the solution was simple, just select the proper databases and remember to save the maintenance plan afterwards 
