ZeroTier One add-on does not connect anymore after restore of full HA backup

This is in regard to the ZeroTier One community add-on for Home Assistant.

I had the ZeroTier One add-on running beautifully in my HA.

I then needed to move my HA setup. So I created a full backup inside HA, downloaded it, and restored it into a different setup.
Everything is running fine, except for ZeroTier.
I tried uninstalling / reinstalling. Even deleted the folder \HOMEASSISTANT\ssl\zerotier. I just could not get ZeroTier to connect to the network anymore (https://my.zerotier.com/).
So I created an image of the original disk (HA was runnung in a VirtualBox VM inside Linux Mint) with Clonezilla and restored it to a different SDD. Same issue.
I even tried setting up a new ZeroTier network and adding HA to the new network.
Nothing.
The Log from the ZeroTier One add-on in HA reports all good.

Side note:
Interstingly, I am not only having this issue with HA, but also with Linux Mint. My ZeroTier One install on Linux Mint worked perfectly, until I cloned the disk image to a different drive. Despite purging the install and deleting folders, I still was not able to add this Linux Mint machine back into any ZeroTier network.
End side note.

My main objective is to get ZeroTier One running again in Home Assistant.

Firewalls don’t seem to be a problem, as I had turned them off for testing when running as a VM. Also, running HA on bare metal didn’t make a difference.

Any ideas are welcome. Thank you.