My OPS .21 Buggy Pro engine also stuck at TDC. It came at BDC, so I didn't know until I crank it with my starter box. Then it stuck at TDC - had to open the head and knock the piston to release it.
I thot it was a flaw from the manufacturer, but have not tried heating it up yet. Thinking of fine scrubbing the top part of the sleeve, but it might damage the coating.
Just afraid it will become a paper weight.