Hey Michael,
Doesn’t directly speak to your timeline render issue and may be something you are fully aware of but once timeline is rendered, you can get some time back if rather than exporting whatever file types needed e.g. ProRes Masters, H.264s etc etc you
1. Make movie of timeline settings. Ensure ‘Make Movie Self Contained’ is unticked.
This will take only a minute
2. Open that file in MPEGstreamclip
3. Make whatever file types/associated codecs needed from there.
MPEGstreamclip is quick, versatile and has the added benefit of allowing you use FCP again without waiting while each export takes place.
Hope that helps.