It already timed-out once (no discernable reason), and after restarting, went right to email number 1 (forgetting about the 1800 emails it had already gotten through).
Regarding the timeout, please send me the error message you had and if it is a bug I will fix it but note that sometimes Gmail cut the connection without any reasons. There is also a retry reconnect process (up to 4 times) if it is not a fatal error (cannot recover from them).
https://github.com/gaubert/gmvault/issues/4
(Issue number 4 on the github project.)
I added my output to the issue.
I'm on Gmvault v1.0-beta from pypi. It doesn't recognize the --restart option. "gmvault: error: unrecognized arguments: --restart"