Just to get the picture:
Were the vocals artificially double tracked=copied and panned to sides or something?
A centered vocal or a "John Lennon" vocal could not cancel itself in any case, AFAIK.
 
If the vocals were phase cancelled by loudspeaker auditioning, then they should cancel also, if you chance the track to mono. 
 
That drums only-case remains a total mystery to me.

The vocals were recorded, centered. No panning at all. The whole ordeal confused me, luckily i just scrapped the vocal track and re-recorded them. No issues at all.

So another unsolved mystery. 
 
Just my 2 cents. I always master my songs in a Wave editor and then I burn to CD and / or convert to MP3. 
Sometimes because I forgot to use "Select None" before export I'll have a song that some tracks are missing from.  If the last thing you edited is still focused ( highlighted in Sonar) then that sometimes is the only item that will be exported. So we need to use "select all" or better yet, "select none" I fine "select none" bullet proof. 
 
I think the mistake your making is not checking your exports with either a wave editor or a  media player.  
Even if it's just a rough mix it's worth taking the time to also do a basic mastering before sending it off.