I followed some recommendations I found in a forum to get Archive to work in Gmail. I set the Archive folder type to Unique and I set the "Gmail/All Mail" folder as the archive folder. Unfortunately this screws up Akonadi, and the only way to fix it is to turn off archiving, do an akonadictl fsck and akonadictl restart.
I'm pretty sure now I was having problems because of: https://bugs.kde.org/show_bug.cgi?id=338658 so closing this. *** This bug has been marked as a duplicate of bug 338658 ***