Can you actually hear them, or are they only on the graphic?

They are very audible.  Vocals sound as though they were influenced by a "Yodeler".

bounce to clip/track?

I've bounced the clips and am not sure the artifacts are affected. The frequency of the spikes is fixed.  I'd guess at one per second.  I don't know why by I suspect Melodyne is to blame! Could there be some truth in that thought?  

Could those spikes be from a percussion instrument?

Just confirming - this occurs in SPLAT and CbB? At what point did you first notice? Could be any number of things - need a detailed repro to help you zero in on root cause.

Thanks Jesse
 
I'm not expert on the DAW but enjoy playing and trying to do with it what I can. I have been using SPLAT to a large extent but I see the spikes in both versions, though I discovered it while using SPLAT. I can give you a copy of a section if you let me have your email address. (For security reasons I hesitate to make it available online for all to see)!  Is that what yo mean by a detailed repro?  Meanwhile I have started a new version since I am basically looking to experiment with  an acapella version of a Christmas Song and am in no particular bind to get it right and under no schedule pressures.

By repro I mean to provide a list of steps that lead to the unexpected result, using enough detail that someone else could possibly reproduce your result. Something like this:
 
1. Record a vocal track
2. Process audio region with Melodyne ARA integration
3. Hit play = everything sounds fine
4. Save and close project
5. Install Melodyne update
6. Reopen project 
8. Hit play
 
 
Results: I hear unexpected yodeling glitches on playback.
 
Something to that effect. :)
 
Just PM'd you to follow up offline...

The artifact (spikes in waveform) only appeared in this single instance.  It is not something that I can reproduce?