Hi John, Sorry for the trouble. The only solution I ever found (I continued with a number of edits after) was to edit each and every Motion clip on the timeline, once you had placed them in. I would recommend you render each clip, one by one (remember saving after each). This wont completely solve the crashes, they will still happen, but less. Also, if you have a big project, and to speed up re-load of project after crash- transfer the timeline to a new project. Then render fro there. Will be qucker to re-start.
Then transfer the rendered clips back (there is a really quick way to do it, using search for ‘motn’ fles, apple-c, then on the old TL, find first motion clip, and press apple-v, sorry havent got time to explain further).
Hope all this helps.