Dear All,
I posted the answer of QNAP support in the wrong thread (sorry).
In short, the NAS has not sufficient memory to process the update. Only manual update is working.
Here the answer:
The root cause is the size of the update files in the database. Because of that the automatic updates are failing on the older NAS models. This is due to the small CPU and memory size.
When you update manually the system get forced to update and will pause other applications running.
So please try to perform the updates manually ones in a time.
Br,