are there stability issues I should be aware of in construct? Is it possible to have too many events? Things along those lines because I don't think the issue stems from the event sheet.
I'm not aware of any issues like that. 700 Events isn't exactly all that big, I've seen users with projects having several thousand (iirc even 10000+) events.
My guess would also be, something mucked up an event somewhere, perhaps just on accident and unnoticed. Classic example: You deleted the boss. If you delete a sprite that is referenced somewhere in an even/action/expression, the action also gets removed. It has to since the referenced object doesn't exist anymore. This absolutely can break your event logic, and it might go unnoticed.
Also, posting the project or at least screenshots of the events in question is always helpful.