What was Chaimistarizog doing in Arc IV?

Chapter I - Song of the Mysteries spoilers here!

In Chapter I of Song of the Mysteries, we learn that the Drake War of Third Age 5867 occurred because Chaimistarizog was challenged and almost mortally wounded and the Fellowship had to step up and hold the line at the North Gate. We also learn that Chaimistarizog never hibernated and still isn’t fully recovered during his final drake duel (as of Third Age 5926).

Back in Initiate’s Trial, the Fellowship wondered why Chaimistarizog wasn’t watching the other side of the North Gate in Third Age 5923. So what was the drake doing 3 years ago that would interfere with being the Gatekeeper?

Posting for discussion’s sake – not a direct ask to Janny (yet!).