I spent a few days editing lots of clips with a lot of those parts speeded up 400%.
I then added a second video track at about the 10 minute mark and enabled multicam editing.
Now all of the previous speeded up parts have audio that is out of sync or some parts are playing at normal speed when they should be speeded up.
In stead of asking here, you can also look in the helpfiles as this one:
What's the easiest way to get back to where I was before.
Can I add the same clips into a new track and use the split positions from the previous track to split the new clips?
Or is there an easier way.
Try it out, I don't know because I first do the multicamerawork and after that I add Effects and other things.
Before I use multicam mode, I always save a version as it is. Then you can revert if something goes wrong such as this.
Because the audio is correct in the out of sync parts I have been able to reconstruct the clips by bringing in another copy of the original footage, speeding it up then matching it with the original audio by cutting the video where the audio is cut.
It's taking quite a while though.
I normally always save a new version of any file before I try something risky, but in this project I got in the habit of just saving over the original when I was happy.
When I first enabled multi camera editing it all seemed to work fine, but I only noticed the out of sync parts after rendering.
Tho only effects that are retained when you enable multicam are those that were previously applied at the Media level. Stretch/velocity applied as Track effects will be lost.
I always save a full duplicate set of tracks on the timeline for contingencies, usually by rendering to new tracks.
Also, "Save Early, Save Often" is especially important in multicam projects.