Sony ZV-E10 autofocus problem in mp4 output

[meridius]

I recorded a theatre performance two days ago. Most of the recording was fine but in a part of it there was one person performing with a photo collage on a screen background and also a map in another section of the recording. This resulted in zooming in and out on these parts of the performance. The problem is similar but worse than this one: https://discussions.apple.com/thread/8259180?sortBy=best

I really don't know how to correct the sections of the mp4 output file of this recording. This problem is shown in the link below. I believe Intelligent Auto or Background Defocus (Defocus and not Clear) was the root cause of this problem.

I normally use DaVinci Resolve for post processing, but I could not find a function in the software to fix this. 

https://mega.nz/file/sGt12SwA#4_pNeW1qPzeV0x6kgLFiHUUykmgKIyPTVSSGbn_ERZs

Many thanks for any advice.

Edited January 5 by meridius

[FunWithCameras]

I don't think it would have been the background de-focus. More likely to be the camera trying to focus on things in the background.

I'm not familiar with this camera, but can you set the tracking to locked-on so it sticks to the performer and ignores the background?

 

[meridius]

This is what I should have done...

The recording of the dress rehearsal was fine and the camera was positioned closer to the stage but I was unable to monitor the camera properly during the show.

I feel really stuck with this problem now and I'm trying to correct it in Davinci Resolve but don't know how to do it.