fcpx 10.9 timeline video corruption / distortion

I did power down the whole system, unplugged power for over an hour. Then powered back. I moved the project to a new library. I moved it to another HDD (external). The error (juggy picture in timeline and export) was still there.

I do have 75% of system drive free.

I created another new library on the editing drive (the same where the error first occurred). I imported the same source files from another footage drive. This time I re-created beginning of the same film anew. All works fine.

It seems that the problem must have happened only in one library, and I cannot copy anything from that timeline to save myself time. The whole film was almost ready and it took many hours to get that project there. Well, I never before encountered anything like this hence my question to others. The only non standard function I was doing here was playing with a larger number of timelapse footages (over 20 clips) where I was re-adjusting their speed to synchro it with beat of soudtrack. There was on or two timeramps there (in and out) with the same time speed adjustment to fit all the footage into beat. Beyond that nothing amazing, no SF/x, no generators, just bunch of titles (4-5) for scenes. All source files in Mp4 (GoPro and AVCHD from XA10 and a pocket AVCHD H264 AAC, and few MP4 clips from a Galaxy A71, so there should not be any footage format issues).

There was no missing files, nor any other issues that I would know about. I only had to restart FCPX with trashing prefs for speed, as it got slow working days on this one project. But there was no issues while closing or opening program or project.

Still puzzled... as when I transfered data from "misbehaving" library to a new library they came even more distorted than in the first place. It seamed like each time I touched the original timeline to do any adjustment, the new glitches were appearing, and the only way out was to undo any changes to the timeline.

What comes to me is that it must have been something I did to the timeline what came through unnoticed that started this "corruption" process... and it had to do with the timing itself (time synchro?) I think, as the more I was doing of any further adjustments (cut, move, retime) it started affecting the whole project. So perhaps if I undo as many changes as possible (not sure how many steps I have FCPX set up to) I could get the whole thing to "fix itself"... But the main question remains...

Is it known to the community if there are any known reasons/situations that could cause this type of the distortion? As I mentioned it seems like my editing (first time I used so much of retiming of the timelapse footage) might have caused it. I just want to learn what to watch for...

I shall try all the received suggestions and will post the results...

As of now I know that this distortion has been written into the project file, as it carried over to the other drive in a new copy of the library, as well as with the data when I copied the project to a new library, but it was not showing in the clip browser of the new library where the "fresh" source files were imported again.

I wish there was a way to peak into the code of what FCPX wrote into the list of instructions. This would help to find the offending code (debugging), but first I shall post what I found after undoing what I could.

Thank you a lot for sharing your thoughts, it gave me some ideas too!

Deleting Render files (300Gb) worked and saved my work. Thank you for the reminder how the basic troubleshooting should be done. I guess I never had any serious malfunction of the FCPX since 2015 with hundreds of edits behind my belt. This says something about this software...

Again thank you for your help!

Thank you for your tip. I never really thought about working on my system drive, but I tried moving copy of the project files to a new library, and it did not help, the error transferred with it, So I tried first the tip from Ben (how could I forget about it... I just never had to do so I guess). I deleted rendered files and after rendering rebuilt the problem was gone and my work saved. Thank you for your suggestion.

Thank you :-D

I have around 70% free of the system HDD, I use only external drives. I edit on RAID (2 HDD) for speed, and all the source clips are on a different HDD as well as sound libraries, and SF/x are on another one. This way I keep drives fast and organized.

Deleting FCPX prefs did not help so it must have been saved in what I have done I think. I was forcing re-rendering (no change), but have not removed rendered files yet... thanks. (I should have done so... how did I miss it?! Thanks). I shall report back outcome of this.