If you have multiple Gmail accounts but are only seeing one offline.
You will need to follow these steps for each account.
Your messages stopped syncing.
You might have run out of space.
Go to Settings > Settings
Click Offline tab.
In the "Sync settings” section, choose fewer days to sync or uncheck the next box to “Download attachments”.
You can’t see email attachments.
When you are offline, attachments cannot be viewed in Gmail. However, you can download them and open them with an application installed on your computer.
Insufficient offline storage error.
Not enough hard drive space.
Using a Chrome incognito tab.
Using a Chrome Guest profile.
Chrome settings are set to clear on exit in Chrome.
Check settings for cookies in Chrome.
On your computer, open Chrome.
Go to More Settings.
At the bottom, click Advanced.
In the Privacy and Security section, click Content settings > Cookies.
Make sure “mail.google.com” or “*.google.com” is not listed under ‘Clear on exit.’