Furu you gotta change them belts! I've had blades pop off from something getting stuck underneath the B57 belt. I would change the bandwheel belts first. And once your blade pops off, in my eyes, that blade is going back to the saw shop to get touched up, I'm not gonna put it back on, unless I had wood or some material inside my blade guards that wouldn't damage the blade. I tried the B56's thinking that it would help, but you break one blade and then theres a chunk of rubber missing and I change the belt. Just quicker/easier with the B57. When I was sawing pine I'd have troubles with sawdust building up underneath them. But I don't hardly saw pine anymore and almost every blade change or so I just pull the bandwheel belts off and scrap the crud off the tops of them with a stout putty knife and run my finger inside the bandwheel groove to make sure it's clean.
So my opinion, forget the B56, get the B57 and make life easier. Have you had any problems since? Was the bark loose? It's possible that a piece of bark, or maybe just a piece of wood (esp if there was shake in the log) came off and wedged itself in between the blade and the bandwheel and spit the blade off. And if it happen around the same spot maybe it could have happened 2x in a row. Not saying it's probable, but it's definitely possible.
Aren't bandsaws fun!