I've seen this kind of writing several times before (I teach students how to write decent stories, not always with any great success if they are a bit dense or close-minded) and I also teach them how to identify and avoid what I know as a Gaping Plot Hole. Any time something needs to have a
crazy set of conditions
|The ritual can only take place on a full moon at precisely the stroke of midnight on the summer solstice when there is also an eclipse... One second past midnight and if you've missed it your entire BBEG's plot crumbles. How easy is that for a good guy to engineer? |
for an event to happen, the character acts totally out of character in order for the story to progress, 'hand of God' type incidences... all are Gaping Plot Holes.
I've read the Timothy Zahn books and I liked them, except perhaps this one where there is the problem the OP describes. To me it sounds more like the publisher decided the story had to end a certain way and the author had to comply, but that doesn't excuse the author from slipping in something earlier to make it not so jarring at the end. Maybe he was on a tight deadline and couldn't rewrite? I dunno.
If it was me, I would have made him redo the work or explain that point in the story much better, because any plot point that happens without a reason that make sense kills the suspension of disbelief as you say, and as soon as a story does that you've just lost your audience.