I just want to add this if someone comes across this thread:
I contacted support (which was a great experience):
My nodes all have ACL tags, which I usually use to define roles. But a limitation of the sharing beta is that shared nodes are only available to “me”, my email address, the owner of the tailscale. But nodes with ACL tags “loose” my identity and are “owned” by my tailscale, so they cannot connect.
So I will have to work around this limitations with having shares and ACL tags.