I can put my finger on exactly what worked but making the file lighter (deleting materials, purging layers, simplifying textures), tuning the settings (rendering settings, viewport settings, SketchUp engines) and starting a new layout file all helped.
I had something fundamentally broken in my layout file, it was like 20x the file size vs a new version that I carefully copied all the annotations and viewports over to.
Good luck, let me know the progress.