I presume this is a brushed DC motor you are driving
in which the waveform looks perfectly plausible.The regular spikey bits are the commutator switching transients, the undulations in the back EMF from the armature are due to the geometry of the motor.The 0V segments are when the PWM is on, the high segments are the inductive kick-back taking thebridge into fast-decay mode at the end of an on period. Only after fast-decay is finished does theback EMF signal become visible (and the switching transients which presumably are inter-windingcurrents being interrupted as the brush passes over a gap in the commutator)
You might try spinning the motor by hand while looking at its output on the scope.
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