Apple Mail is not downloading all mail from Google Apps account but my IOS devices set up as exchange do

My Apple Mail on imac is no longer is syncing properly with my Google Apps account. It syncs some of it but not everything. This account is set up as an IMAP account.

However, on my IOS devices (iphone and ipad) where the same account is set up on EXCHANGE it is syncing perfectly.

I have tried the following:

• Rebuilding the mailbox;
• Changing the Google Apps labels;
• Deleting and setting up the account again;
• Shutting mail off and relaunching (several times).

But nothing seems to make a difference. I do have other Google Apps accounts that don't seem to be effected.

Has anyone experienced this before or have an idea why it may be happening?