Have you updated Premiere Elements 12 to the 12.1 Update using an opened project's Help Menu/Update
or whatever the Mac counterpart is for that.
I am strictly an Elements Windows user.
Have you tried to install the Premiere Elements 12.1 Update? If so, have you run into problems doing that? If so, please
Please review and consider, and then let us know if any of the above targets your question.
We can also take an in depth look at your Timeline content and project setup to determine if any of your crashes are
related to them. Lots to explore, but first the 12.1 Update.