Ubuntu client remains "Logged out" on a dual-boot laptop until old device registrations are removed

### What is the issue?

## Summary

While setting up Tailscale on a dual-boot Windows + Ubuntu laptop, the Ubuntu client repeatedly remained in a "Logged out" state even after completing browser authentication.

Removing all existing Tailscale device registrations associated with that laptop (both Windows and Ubuntu) and then authenticating again resolved the issue.

I'm not sure whether this is a bug or expected behavior, but I wanted to report the experience in case it's useful.

---

## Environment

- Laptop: Dell
- Operating Systems:
- Windows
- Ubuntu (fresh installation)
- Boot configuration:
- Dual boot (GRUB)
- Tailscale version:
- 1.98.9

---

## What I observed
- The Ubuntu machine briefly appeared in the Tailscale desktop application on my Mac.
- The admin console either showed it as offline or as an unknown peer.
- Ping between devices did not work.
- Re-running tailscale up did not resolve the issue.
- Reinstalling Tailscale also did not resolve it.

## What eventually fixed it
I deleted every existing Tailscale device registration that belonged to this physical laptop, including:

the previous Ubuntu registration
the previous Windows registration

After removing those old registrations, I authenticated Ubuntu again.

This time the client remained logged in and everything worked normally.

Expected behavior

Either:

the Ubuntu client should authenticate successfully without requiring previous device registrations to be deleted,

or

if this behavior is expected, some indication of why authentication cannot complete would make troubleshooting much easier.

### Steps to reproduce

## Steps I performed

1. Installed Ubuntu alongside an existing Windows installation.
2. Installed Tailscale on Ubuntu.
3. Ran:

```bash
sudo tailscale up
Opened the authentication URL and successfully logged in.
After authentication, running:
tailscale status

continued to report:

Logged out.

### Are there any recent changes that introduced the issue?

NO

### OS

Linux

### OS version

Ubuntu 26.04 LTS

### Tailscale version

1.98.9

### Other software

NA

### Bug report

_No response_

Start by reproducing the dual-boot setup and the reported command sequence: run `sudo tailscale up`, complete the authentication URL, and check `tailscale status`. Compare behavior before and after removing the Windows and Ubuntu device registrations. Done means determining whether stale registrations cause the Ubuntu client to remain logged out and, if so, exposing a useful indication or documenting the expected behavior.

Written by the indexing model from the issue text.