Because these are often "temp" files, they may not play in standard apps like iTunes or Spotify if the recording app crashed before saving the final metadata. Common Sources of "RecordTMP" Files
Apps like GarageBand or Audacity may create .tmp or RecordTMP files while you are recording to ensure data isn't lost if the program closes unexpectedly. How to Access or Fix the File RecordTMP (32) m4a
How to Recover Corrupted Audio Files