Many Schottky devices are not avalanche-rugged.
The 3A rating, if this is the low side catch-diode of
a cheap buck controller, seems inadequate against
your 10A motor current (which it must carry for the
duration of the "low" phase, violating a time-averaged
If rating at anything over 30% duty at 10A).
'Scope waveforms ought to tell whether this is a
current or voltage induced failure. A finger on the
rectifier will tell you if it's power dissipation. Heh.
Which, 10A*1V*(1-duty), can't be ignored either.
What the datasheet says can be handled for V (I=0)
and I (V=Vf+?) is not what can be handled at once
and what can be handled, depends on how helpful you
were regarding cooling.