Since I upgraded to Yosemite on January 3rd, my Apple mail app is misbehaving. When I get new messages from gmail, they show up in the Unread and Today mail folders but not in the overall Inbox folder. After they are read, they disappear from Unread (of course) and are lost in the ether. If I search mail for a specific message, it finds it and indicates its either in an Important folder or simply in the inbox. Otherwise the message doesn't show up in Mail at all. Also the mail remains on the gmail server when I access it directly on the web.
I've tried to synchronize the mail accounts but nothing changes.
I also turned on iCloud and iDrive at the same time.