This bug happens unpredictably and far too often whenever I have more than a few graphics throughout a timeline and (usually) when I have a chromakey on the primary timeline.

All of a sudden, without warning, I will completely lose the visual from the primary track at certain junctures during a video. The background is visible. Image overlays usually still appear. I can even hear audio - but no video. This has happened in multiple projects over the course of many weeks, and I extremely frustrated by it.

Has anyone else encountered a similar issue? I'm running 10.0.5 but I've had the issues probably since 10.0.3.

What OS X version, what Mac model, what are it's specs, what's your hard drive configuration?

Same problem periodically occurs on two different machines on many different projects:

Machine 1: 2010 Mac Pro Quad-core, 12GB RAM, OS X 10.6.8 , 7200 RPM main drive

Machine 2: 2011 MBP i7, 8GB RAM, OS X 10.7, SSD + 7200 hybrid drive

These are different FCP X installations (obviously).

Never seen that sort of problem before.
Are you using any third party plugins?
What GPU in the MP?
What codec are the video clips? Can we get a screen shot of the project Timeilne?
Are you putting Events and Projects on your OS drive?

Very odd indeed.

Be sure background rendering is turned off in the preferences.
Use Digital Rebellion's "Preference Manager" (free) to trash FCP X prefs safely and quickly.
Verify all hard drives have at least 15% of their total capacity as free space.

It happens nearly every time in the course of a more complex project, but there doesn't seem to be any rhyme or reason (e.g. why does it happen to a random clip along the timeline? why does it sometimes happen simply by scrubbing with the playhead? or other times merely by opening a project after a few days?). Occasionally I'll get it fixed by using the "break apart clips" command, which is admittedly inexplicable.

A related issue is that secondary "tracks" - i.e. graphics or clips I've dropped in above the primary timeline will occasionally "drop into" the main timeline and actually cover up the primary video, creating a whole host of silly playback issues. Considering this isn't even how the dynamic timeline works, it is definitely not intentional.

I do love FCP X, but these little bugs drive me nuts. I'm deathly afraid someday I'll lose a whole project to some mysterious issue.

If I can get that info...

Are you using any third party plugins? No.
What GPU in the MP? Radeon 5770.
What codec are the video clips? I transcode all video to ProRes (optimized).
Are you putting Events and Projects on your OS drive? On the MP, yes. On the MBP, no.

Given that it happens on both of my vastly different machines, I don't see how it could be a hardware issue. And given its randomness, it sure seems like a glitch. The next time it happens I'll get a photo grab (I fixed the last one by breaking apart the file).

Yep, that's odd. All the systems I work with weekly, never seen that. Very odd.

I've seen that exact problem. In one case it was because the user hadn't fully imported his clips from a camera archive. You could tell because the clips in the viewer still had a camera icon on them.

The other time was because the graphics were huge and 300dpi.

I think it does have something to do with FCP X's admittedly tenuous relationship with graphics (and titles, for that matter). Sometimes they play nice; other times I get the strangest glitches imaginable. No project has been entirely unsalvageable...yet. But it's still annoying when it comes up.

Hopefully future updates will improve these sorts of finicky interactions.

I've done two projects using 300 or more in each 4K graphic images. It was a bit of a bear to deal with, but I had no disappearing video.

Sounds like you might be seeing some orphaned frames which can happen intermittently with applied transitions that attempt to span clips without sufficient handles (if I said that right). This has been an ongoing bug of sorts since 10.0.2 (maybe earlier), although I haven't seen it myself in 10.0.5.

Next time you see the problem, expand your timeline very large and see if you have any unwanted clips or slivers of clips in that area of your project.