Synching problem on export

When I export my timeline (not a compound clip).
For some reason audio get's slightly out of sync. 5 to 6 frames.
I was wondering if it was best to export a compound clip.
Did anyone face this problem on export?
I did check and everything is sinched on the timeline.

Thanks

Timeline duration?
What codec are you exporting as?
How are you playing it back?
Mac specs?

21:07:13 A bit over 20 minutes
MPEG 4
I use QT to read it.

Would compressor give me more export options and better quality?

If this is 4K output, could be a playback issue. If not, hhhmmm....

No, Compressor uses the same engine. But do a "Send To Compressor" as a test.

Not 4K. Simple 1080.
I don't have compressor .
I will keep you posted as I try to solve this.
Thanks.

List of normal troubleshooting steps:
- Select the Library in the Browser, go to the File menu, to Delete All Generated Library Files and delete ALL render files.
- Quit FCPX, launch again while holding both Option and Command keys down together to delete preference files.
- Go into Preferences and turn OFF background rendering, and never turn it on again.

I think I solved it.
When you noted about playback I checked on my laptop and It is a playback issue on my laptop.
I will delete the render files as suggested.
I never use background rendering so that's done.

Danke.

Yeah, I use "Final Cut Library Manager" and regularly delete render and cache files across the board on all Libraries. Saves me tons of drive space.

I have an old 2013 rMBP and it struggles with 4K.