When you played vs the AI online, there is no OOS because you're not being synchronized to a remoted computer as when playing vs other human opponents.
What Out of Sync is, is basically when a player (or players) have modified game file(s) that make the computers not agreeing with each other.
From my experience of getting the OOS, I know there are a few reasons that cause this to happen:
1) having mods of existing units/techtree
2) Water/Forest.xmb that has not been updated with the expansion's materials
and possibly
3) having moddified animation files (when installing reyk's new editor, the instruction mentioned about OOS with modifying animations.)
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So when you had these OOS, it's difficult to tell which one of the players caused the OOS. It could have been you... or the other players you were playing with.
A good way to find out is by simply test with one player, so it would be easier to narrow down what the exact cause of the OOS. If you would like to, I can test it out with you probably tomorrow night. (My time zone is US Pacific)
My ESO name is: Greeks___
(3 underscores)