Removing or Relinking Project Files In Premiere MAY Cause Media Files To Cease Linking. READ ME
If you remove / relink project files when you still have that project open, certain files will not relink properly and you are forced to do a premiere restart in order to fix this.
I have attached a screenshot showing how the Waveform of the audio file disappears if you zoom too far in, which is very annoying, but more importantly the file in question stops playing altogether. It will still appear to in the project though.
Even if you do a "Media Offline" and relink pass, the file still will not be detected. For whatever reason, the project needs to be restarted to fix this.
I am able to reproduce this by doing the following actions:
1) Moving said audio file to another location inside the project folder.
2) Deleting other similar audio files from the project at the same time.