Just to confirm, this patch worked for me as well. I’m using two Linux (Debian 10) V-Server from STRATO (happarently hosted on a “virtuozzo” based hypervisor. Adding the “-U” option to the " ExecStart=/usr/sbin/zerotier-one -U" line in “/lib/systemd/system/zerotier-one.service” did the trick.
Best regards
Yonz