After I ran apt update zerotier-one on one of my debian machines to go from 1.4.6 to 1.6.4 I had ONLINE on my.zerotier.com network, but OFFLINE after running sudo zerotier-cli status.
I resolved this by purging zerotier-one
sudo apt purge zerotier-one
Then I had to delete the folder /var/lib/zerotier-one folder to remove my old secets and node info etc. PS only delete from the terminal if you know what you’re doing, I take no responsibility for you running this command.
sudo rm -r /var/lib/zerotier-one
Then reinstalled zerotier-one
sudo apt install zerotier-one
Then rejoin my network
sudo zerotier-one join $NETWORKID
Opened my.zerotier.com to delete the old node, then add my required IP to the new node and then authorise the new node.
Then check my status to see I was ONLINE on my machine
sudo zerotier-cli info
Hope this can help out the next person along