10.4 Terribly Slow Export

Decided to upgrade and purchase FCP 10.4 and I'm regretting it big time.

I need this professionally and now I'm in a jam. The export speed is now terribly slow. Like hours to do a 4 min video. It used to be way quicker with the previous version I used..I forget the version, 10.2.X maybe or 10.3.

Regardless, I upgraded the library for 10.4 and now I can't open it with the old version. Probably can't get a refund anyway on the colassal amount of money I spent on this, only to have my business severely impacted.

Does anyone know a fix for the slow export/rendering? It's working fairly well for me besides that.. But I need this to export larger length videos, which will surely take days.

Any help appreciated. Thanks.

Using a late 2014 Mac Mini and Sierra now. Upgraded to High Sierra which was a nightmare in itself, so I downgraded hoping the FCP problems would resolve, but no luck.