Lost Gmail inbox, can't restore with TimeMachine Friend woke up today to find only 15 of his 9000+ emails in his Gmail Inbox. Have confirmed on iPhone and Gmail website that for whatever reason, these emails are gone -- they don't show up in "All Mail" and they aren't int the trash.

Compounding that, although his TimeMachine backup has been running, when I go to restore for him, there are two problems preventing him from actually restoring anything. 
1) when choosing a date/time on the timeline, although the email count changes, the screen doesn't animate
2) the Restore button never becomes active

If I try to restore something in a Finder folder, TimeMachine restore works fine.

Has something changed in El Capitan that prevents email from being restored? perhaps due to it being a Gmail or IMAP account?

Running Mac OS X 10.11.4
If it is an IMAP account (don't know if GMAIL accepts POP3) I'm afraid the Time Machine is useless because those mails were not in the local storage - your HDD or SDD, so there is no way Time Machine keep it in backup files. This emails was in a remote Google server and you will have to try their recovery tools.

Usually, the server will keep the deleted messages for a while, even not showing in the trash. This is good place to start: Google Support