You'd do best to file this via the feedback form, and include your crash log there in the comments box.
You could try a reinstall.
But for "many multiclips" I'd start optimizing media for them. And the GPU in that rMBP isn't the most powerful around. You may want to get Event Manager X and hide the events and projects you aren't currently using.
You may have some corrupt files.
And having many large events consumes a lot of ram and slows down FCP X - as you have been made painfully aware!
Consider hiding events that you are not using.
You can do it with Event Manager X, but you can do it manually very easily.
Create a folder called, say, "Final Cut Events - hidden" beside the normal "Final Cut Events" (and likewise for projects). Move the stuff you don't need there. FCP X will not load them and will start much faster, use less ram and maybe avoid some of the problems that you are encountering.
At the very least if it crashes you won't waste so much time.