File has HE-AAC v2 audio track. Maybe Resolve doesn't support HE-AAC, just AAC audio. Your file is from mobile etc. with variable fps. Bad recording for use in Resolve.
You may want to put it through ffmpeg:
ffmpeg -i source.m4v -r 30 -c:v copy -c:a pcm_s16le out.mov It's very fast conversion changing audio to PCM and copying video untouched.