I am running Tailscale 1.4.5 on a Raspberry Pi Zero W that uses a cellular connection to reach the internet. On boot, tailscale starts, and then I run a script that connects to cellular and sets the default route for the cellular modem.
With this setup, I cannot ping / ssh into this machine (“devpi”) from my desktop Mac (“jmac”) until I SSH into devpi directly and then use tailscale ping jmac. Once I ping, then I can reach devpi from jmac (which is also running 1.4.5). Otherwise, this doesn’t work. I have been able to get this to work sometimes by calling tailscale down && tailscale up after the default route changes, but it doesn’t always work.
Can you share your script that changes the default route to the cellular modem?
If we can reproduce this it’ll be a lot easier to fix.
I deleted my original reply because I included a little too much. Basically, this is the gist – I add a ppp0 connection, then run the following with sudo:
route add default ppp0
ifconfig wlan0 down
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Hi SupportBot… I’m on Linux, not Windows - don’t think this applies. 
@jdelman, I’m curious whether our recent link monitor propagation work happened to fix this in our upcoming 1.6.0 release. (which should be out early next week)
Can you try a pre-release build in the meantime and let us know? https://pkgs.tailscale.com/unstable/
I’m curious if this was resolved or not.
If I recall correctly, this was the symptom of a DERP issue (meshing between derps not always working correctly) which was resolved last year.
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