Synology Container: No connection nor ping to / from SynologyNas

Hi all,
I am brand new to Zerotier and installed it on a docker container on a Synology DS920 following the official installation guidelines for DSM7. There are 3 devices linked to the network - the SynologyNas, Computer and phone. The are all assigned to the ZT network. Firewalls on the PC and Synology are turned off (only for testing purposes). All version are the newest available ones, just downloaded today.
I can neither connect nor ping from the Computer the Synology or vice versa using the ZT IP-Adresses with message from Synology to PC “Destination Host Unreachable” and from PC to Synolgy “Destination Network unreacheable”. If I check the peers from the cli, it shows 3 with role LEAF and DIRECT links. I would be greatful for hints. Thank you in advance