There are a few reasons why comments may not be appearing on your track. 
 

Quiet Mode

If you have a Next Pro subscription, please check to see if you have enabled Quiet Mode on your track. If you have Quiet Mode enabled, it will hide comments from appearing on the waveform and track page. You can check to see if Quiet Mode is enabled through your track's edit page in the Permission tab. 
 

You replaced your track’s file

If you have a Next Pro subscription, and recently replaced your track’s file to be a shorter version, don’t worry. The comments on your track that were on the previously longer portion of your track will still appear in the comment’s section, but won’t show avatars on the waveform. 
 

Comments were deleted

If you got a notification that someone left a comment on your track, but when you go to your track’s page it isn’t there, that means that they have deleted the comment before you could read it.