Shooter accidentally enabled Off-Speed Frame Rate. Fixable?

Hello! I am in need of urgent help.

I recently took over editing a project that the previous shooter/editor was fired from. They accidentally enabled Off-Speed Frame Rate on the footage, I believe.

Footage frame rate is 24fps. On timeline, footage looks slightly slow-motion, but audio is not distorted. Audio is not synced with footage, and slipping audio does not fix.

Does anyone have experience with fixing this issue in post?

Thanks in advance!

There's no single adjustment which will bring picture and audio into sync. You'll need to do it manually, like in the old days when the camera or the recorder lost crystal sync.

What's your timeline fps? Anyway, that was one good reason to fire a shooter.

I keep the off-speed rate at a very different value, so it's easier to notice if you accidentally activated it.

If your video is not really shot at 24p and you need 24p then there is no easy fix. It's basically the same as if you shoot at 30 and needed it at 24p. Fps conversion is the only (if you need realtime video) way and this always has side effects.
You would need to know actual shooting fps (probably 30?) and then set this in clip properties and export some pre-graded footage from timeline at this fps (this way you get realtime footage).
Then bring this into 24p project, set optical flow fps processing and pray for good result At this moment you will be in realtime speed so original audio should sync perfectly.

If the timeline is 24fps, the project frame rate is 24fps and the off-speed rate was 24fps, off-speed footage still won't be in sync.

Like everyone said, there is no easy fix and if you can fix it, there can be some other issues you'll have to contend with. One option, albeit not a good one but could save your day, is to just process the entire footage at the off-speed frame rate. If your off-speed rate is 60fps, try setting your timeline to 60fps and render at that rate. If you originally intended it to be shot in 24fps, well you'll lose things like motion blur and other artifacts at 60 but you could save the footage, and the day.

Of-speed in camera just sets headers to 'desired' fps, while recording at other one.
It's the same as recording at that other fps and later assuming desired fsp in Resolve clip attributes.

There is really no other fix. It's the same if you would record by mistake at eg. 30fps instead of 24p.
You just have even more mess because your file says it's recorded at 24 which is not true.
I actually don't like of-speed recording in camera.

And I don't like the way the HFR button is placed (and that it can't be deactivated).
Other camera manufacturers offer a similar feature, but of course you could aways change the fps in the Clip Attributes.

Footage frame rate is 24fps. On timeline, footage looks slightly slow-motion, but audio is not distorted. Audio is not synced with footage, and slipping audio does not fix. Does anyone have experience with fixing this issue in post?

I've fixed it, but it's unpleasant, frustrating, and time-consuming. Did the camera operator shoot all day with the wrong settings, or are some of the takes OK and some bad? This kind of thing used to happen in the film days as well: we'd have one camera at 24.00fps, another at 23.98, another at 25fps... weird things can happen.

I'd say this would be a question of experimentation, trial & error. Try different speed changes and see what syncs up and stays in sync. Once you find that magic number, you'll need to use Optical Flow to solve the visual artifacts; Optical Flow -> Enhanced Better usually works pretty well. Once you have that speed rate, there's a good chance it'll hold for all the shots that are bad.