Nautilus-dropbox suddenly stuck ("Starting...") after reboot on four different machines

I have four different Ubuntu 24.04 machines that have all been running nautilus-dropbox successfully for months to years, some since Ubuntu 20.04. Starting some time last week, they all successively stopped syncing after reboot. I am not aware of anything that I changed (and it doesn't seem likely that I changed anything on all four machines).

My dropbox status, even after hours, now always says:

```
🌑 dushoff@siX:~/screens$ dropbox status
/usr/bin/dropbox:613: DeprecationWarning: isSet() is deprecated, use is_set() instead
if self.stop_event.isSet(): break
Starting...
🌑
```

`dropbox update` succeeds but does not change the situation.

I get occasionaly warnings about fs.inotify.max_user_watches, but this seems to be a red herring. Warnings don't always stop even when I increase this value well beyond my folder number, and behaviour doesn't change even when the warnings stop.

Here is some more information:

```
🌑 $ lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 24.04.1 LTS
Release: 24.04
Codename: noble
```

```
🌑 $ dpkg -l nautilus-dropbox
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-================-====================-============-========================>
ii nautilus-dropbox 2019.02.14-1.2build2 amd64 Dropbox integration for >
```

I'm not using firewalls or vpn. The machines are in two different physical locations (two at home and two at work).

I tried the dropbox "headless" approach on one machine. This installs but produces the same forever "Starting..." behaviour. I tried other things, but this one seems potentially relevant to the nautilus-dropbox problem.

Begin by reproducing the persistent “Starting...” state with `dropbox status` after reboot on Ubuntu 24.04, comparing the packaged `nautilus-dropbox` installation with the headless approach. Inspect `/usr/bin/dropbox` around line 613 and review the reported inotify warnings without assuming they are causal. Done means identifying the cause and verifying that Dropbox resumes syncing after reboot.

Written by the indexing model from the issue text.