Weird FCPX artefact after rendering (pic included)

I have noticed this weird rendering issue in FCPX. I believe I have seen it in playback occasionally (and randomly) too. You can see the weird pixels. Any ideas how to stop this?

Could you post a screenshot?

Apologies, I posted on mobile and thought it had uploaded.  I've now edited the original post.

I noticed another.  Exactly the same glitch.  Also, interestingly on text too.

Is this during playback in Final Cut, or are these files that have been exported?

These are 4k exports. It's a normal fcpx "basic title" for the font.

What are your output specs? You say 4K... is that a built-in preset, a master ProRes file, a custom Compressor setting?

If you could specify codec information, datarate, container type... and if this is an internal or external drive you're rendering to. And some machine specs, OS version, FCP version. Sounds like a lot, but is all helpful information for tracking this stuff down.

Side note: Basic Title isn't a font, it's a text overlay template where you can choose the font that you want in the inspector. Looks like maybe Helvetica. A corrupt font could maybe cause this - if you render out the same project twice, does the corruption show up in both files, and in the same places?

Hi there, thanks for replying.The artefacts do appear randomly, and not the same on each render.  I’m not certain it’s only on render - it might be happening occasionally in playback too, but I haven’t verified that yet.  Note - there were 2 frames with an error in a ten minute video and it literally only on the screen for one frame.  Blink and you miss it.  The thing I’ll try next is to use H264 Best Quality as opposed to faster encode. Any other ideas would be great.  P.S As you say yes it’s a standard font in a container.  Settings:Share apple devices 4K (3840x2160) 25 fps.  H264 Faster encode, Color Standard Rec. 709.  FCPX Version 10.6.2Os 12.3.1 2019 Mac Pro3.2 Ghz 16-Core Intel Xeon W192 GB Ram.

Follow up: I just had this happen whilst working on a project, not a render. Furthermore, it happened over a random part of the screen and not over text. The plot thickens...

Can you give the complete specs of the media and the project properties? What computer is this? Are you always seeing this precise patterning?

Hi there, it’s FCPX Version 10.6.2 on OS 12.3.1 .  It’s a specced out 2019 Mac Pro 3.2 Ghz 16-Core Intel Xeon with 192 GB Ram.  I’m not sure what you mean by the media and project properties but it’s 3840x2160 at 25p, Rec 709.  Rendering is Apple ProRes 422.  Please let me know if I’m missing specifics here.  To answer your question: yes the patterning is always diagonal pixels but varies in size.  It is also usually on screen for 1 frame only, before disappearing.  
Ps sorry about my formatting  - this forum is impossible to use on mobile  😂

Tom is asking about the format of your source footage. Size, codec, container (even the camera could be helpful).

Sounds like your timeline is 4K 25p ProRes, yes?  Already answered.  

The camera is a Gopro 10 but it's not always that footage that makes it glitch.

That’s right.  The footage/archive in the project definitely has different frame rates, but I’m assuming FCPX is making things play at the host 25 FPS?  I’ve looked further - there are 3 places I have seen this digital glitch so far, one where there is a 30 FPS video playing in the timeline, one where there is a 59.94 FPS video playing in the timeline.  However, I also saw the glitch at a point where there is just a 25 FPS video, and a 25 FPS compound clip of text boxes… so maybe that isn’t the issue?