H-Bridge with Darlington BJTs, static shoot-through
I've had more problems with breadboards than you can shake a stick at !!
Many a time,the problem seemed to be un-sound mechanical connections.-and this is NOT just one single board,this has happened on a few of them.Breadboards are great when they're new,and clean,but after a while,they get contaminated with all sorts of debris and dust,etc.It may seem like a long-winded solution,but I'm fairly sure that if you clean your component leads,and solder the circuit together (p.c.b or vero),the intermittent fault will disappear,and all will be good with the world.Oh,and unless you have an ultrasonic cleaning bath to clean your breadboard,chuck it out and buy a new(clean) one !!