Reasons are the same as those that led to changing naming scheme in https://forum.obsidian.md/t/obsidian-release-v0-8-15/5697
Pasting images now use a 14 digit timestamp format “Pasted image 20200914050118.png” instead of a regular number “Pasted image 15.png”.
For audio-recordings produced by the Audio Recorder plugin:
use naming scheme equivalent to scheme for pasted images.
Just avoid spaces in filename, to avoid later issues with encoding, enclosing in quotation marks, etc
Rename each file manually.