I’ve experienced 3 bug splat crashes in the last hour on SkepchUp 2018 Pro for my Mac- the first after 2 hours of very detailed work that I must redo now. Why is there no backup for unsaved documents when I relaunch the program?? This seems like an issue that should be fairly simple to resolve by a program technician.
Do you have Auto-save and Create backup turned on? Those settings can be found in SketchUp>Preferences>General.
SketchUp is not the most stable SW but it shouldn’t crash that much (or any SW is practically unusable at that rate). Fill-in your information and maybe some of the sages here will see if there’s a problem between the MacOS version and the SketchUp version. I am using Mojave and SketchUp v.19 and I think most crashes I see involve Twilight renderer. (As a precaution disable plugins you aren’t likely to be using in a session).