Some emails dissapeared from gmail (in range of Apr 23, 2013 back to Sep 8, 2012)

I use IMAP protocol to get emails. I did not use off-line feature at the time (now I do). Emails disappeared right after installing a patch on May 16th. I haven’t done any email cleanup recently. Emails disappeared from on-line gmail account as well.
Sent emails did not dissapear.
All emails are in place for my other account (IMAP+offline).

Best Regards,

Can you please login to the mail account in a browser and check if the messages are still present on the server? Thank you.

No, all gone.

I am afraid I cannot provide you any solution at the moment. If the messages are not saved on the server, they have been probably deleted. Do you access the account from multiple devices? Did you check the Trash folder?