ffmpeg – concatenating list of mp4 getting Error parsing the packet header and other errors

I have a number of mp4s that were in some cases converted to mp4 from other formats using ffmpeg.
Now I want to concatenate these files into one.
I decided to use the concat list method

ffmpeg -f concat -safe 0  -i list.txt -c copy out.mp4

which ended up giving me the

Non-monotonous DTS in output stream previous current changing to This may result in incorrect timestamps in the output file

error.
So then I tried

ffmpeg -safe 0 -f concat -segment_time_metadata 1 -i list.txt -vf select=concatdec_select -af aselect=concatdec_select,aresample=async=1 out.mp4

and I got a bunch of errors

aist#0:1/opus @ 0x12f6109b0] [dec:opus @ 0x12f66f4f0] Error submitting packet to decoder: Invalid data found when processing input
[opus @ 0x12f6702a0] Error parsing the packet header.

And the video is choppy, bits cut off, and the audio sounds like cheerios being eaten.

I’m not an expert in this area, obviously so I am at a loss to fix it. I would expect that there was a setting to say – take the formatting of the first video in this set and apply it to all the others, convert audio to audio etc. But don’t cut off the time.