Toilet started wobbling
The best approach here is (as @DMoore mentioned in the comment) to pull the toilet out and re-seat it.  Not only will this let you see if the ring is cracked, it will let you get the tile spacers that it is currently shimmed with out from under the toilet.  Also, once a toilet starts rocking it is only a matter of time before the wax ring get moved around enough that it will start to leak.  You'll want to replace it to ensure that it hasn't already been compromised.  

I'm guessing that this is more a problem with the shims themselves than it is with the ring (but again, you need to verify this).  Most of the tile spacers that I've worked with when laying tile are made out of nylon, and they are slightly compressible. So, every time you've put weight on the toilet it has deformed them a tiny bit until they became flat enough to let the toilet rock. Once you get to this point, even if the rocking is imperceptible it lets them start shifting around underneath and it snowballs from there.

Once you get the toilet up and make sure that the ring and bolts are OK, re-seat it with proper shims.  You'll want something that can support quite a bit of pressure without deforming to shim it - I use composite plastic shims: