Experiencing choppy video playback in FCPX since updating to Catalina 10.15.5

True to my word, I would now like to share the solution. Yesterday, I tried the very first thing that Luis had suggested — trashing Preferences. Many video forums list this as one of the first things to try in order to solve playback and other performance issues. At first blush, this seemed to work somewhat — playback was still intermittently choppy but not quite as bad as it had been. I continued work on the project at hand and was dismayed and alarmed when within a few hours of trashing the Preferences as Luis suggested, performance got dramatically worse. FCPX crashed repeatedly over the course of the next 24 hours, sometimes five or six times an hour — mostly when image stabilization was applied, but also during routine editing. I was considering exporting the project to another editing system when something remarkable happened: Apple issued a Supplemental Update to 10.15.5 about an hour ago. In my original post here, I opined that the 10.15.5 release had been the cause of my choppy playback issues — so I immediately installed the Supplemental Update. Bingo! Problem solved. No more crashes, no choppy playback. As usual, the whole fiasco was my fault — I have an ironclad rule to never upgrade system software until at least a month or two after it is released, but I broke it in this case. FCPX seems to suffer more than most apps from upgrade-itis. Bottom line, there was no need to buy special diagnostic software, and no way that any conventional fixes would have worked — once Apple released the patch for their upgrade, the problem was solved. 

I think I've managed to solve the problem and if the solution holds up for another week or so, I will post it here. For what it is worth, I'm on a Mac Pro (black trash can style) running 10.15.5 with an AMD FirePro card. The media I am working with is just run of the mill mp4 files shot with a Lumix 4K camera. I am using the exact same setup that has worked like a charm for me for the past six or seven years. The only difference has been the upgrade to 10.15.5. Prior to that, everything worked without a hitch. After the update, crap video playback in FCPX and VTDecoderXPCService going through the roof. I downloaded Etrecheck as advised, and while the download is indeed free, the free version is just a come-on to pay them 15 bucks. On top of that, one of my AV programs flags the app as potential malware. Thanks to all for your comments and ideas.

Sorry Luis, no sale here. My AV apps work just fine, thank you. And a quick search brings up multiple posts about Etrecheck smelling funny. Like this one, for instance: https://sites.google.com/site/howtotellifyourmacishacked/is-etrecheck-malware

In any case, I appreciate your willingness to help, but as I mentioned, I seem to have stumbled upon a solution. Best regards.

Will share it when I am sure it has worked as it seems to at first blush — as I said prior. You seem to be very upset about something, Luis. I am genuinely sorry if in seeking help here, I have offended you, or broken rules you have set for this community. I have no further answers for you, so please, go ahead and have the last word.

Thanks for your comments, terryb. For what it is worth, I am already familiar with the helpfulness of the two gentlemen you mentioned. That's one of the primary reasons I chose this forum to ask for help. I have seen Tom's helpful answers in other video forums as well. Again, thanks.

Thanks for your suggestion but Settings were already set to better performance.

Thanks for your suggestion, Luis, but I am not interested in purchasing software to solve this issue.

I will let you have the last word on this, Luis. Thanks for sharing your thoughts.