pwhooftman synology based on the ova file from Gommunio
I also set up the OVA on a DS in the VMM at the beginning and had adverse experiences. Since then I only install a VM in the Synology VMM based on an ISO which was imported into the VMM.
During the installation I do not allow to the setup to update the system as this has also led to errors. Only after the installation is completly done I allow system updates.
By the way, if you know German, there is a Grommunio thread for this in the Synology forum.
https://www.synology-forum.de/threads/grommunio-for-synology-g4s.124600/
In my experience ActiveSync does not work with Grommunio, only Exchange based protocols or MAPI. For example, I use Outlook on Windows and Nine APP on Android.