FCP X very glitchy

I have been editing with FCP 7.03 on my 2014 I Mac running OS 10.10 for years. It's stable and works like a dream. Just finished a 1 Hr 20 min video with lots of stills in HiDef. The waiting to render is killing me! Yesterday (11-11-17) I updated the OS to HS and downloaded the latest FCP X and Compressor. What a mess! FCP is glitchy and I can't get Compressor to open Create Disc to burn a Blu Ray. Yes, I set the inspector to create blu ray and tried everything including adding a background image as was suggested after a previous post. I've been doing lots of reading and others are having the same issues with HS. Does anyone know if it's possible to get/buy a copy of OS 10.11 or OS 10.12 which is reported to be stable with FCP X and Compressor? I took my I Mac. back to OS 10.10 and FCP 7.

Thanks,

Henrik