Lots of input on tramming here, but I think the main issue is clearly that the bit went into the piece. You can sand away ridges, but in my experience it’s much harder to put wood back where it was 
I think @gdon_2003 is correct on losing steps. @WillAdams , is there any ballpark material removal rate that definitively loses steps? I mean, I know it’ll be particular to the machine, bit, etc… but is there some rule of thumb like: this depth/overlap/feed rate is almost certainly “too much” for a Shapeoko?
I had a very similar experience I shared on this bowl I made, but the cause was quite known. I looked away for about 1 second while holding my shop vac hose close to the bit to help with chips and the machine came around and bumped it. Bye bye 
Both of our symptoms seem to align… it’s just a matter of how yours happened, as there’s no obvious cause. It’s interesting that (a) it made it all the way around (why wouldn’t it lose steps early if the cause is overloading the machine?) and (b) after side grain, as I think end grain at least sounds way tougher on my machine.