On reboot of my opnsense router it did not tailscale up. I'm not sure if a key expired or what happened. The fix was to first enable ssh, then ssh in and run tailscale up.
enable ssh
In opnsense System > Settings > Administration > Secure Shell > Enable Secure Shell
tailscale up
ssh <opnsense ip> 8 # to select shell tailscale up
Follow the link to log in.
disable ssh
now uncheck secure shell to lock down the opnsense machine.
In opnsense System > Settings > Administration > Secure Shell > Enable Secure Shell