Do you put your forms in an oven?? How many degrees??? Do you ramp up the heat fast or slow and steady??
I don't think I put that one in the oven ever.
My hot box takes 1 hour to come up to temp. with the form in. 180*
Check your forms with a long straight edge.
With the high reflex and static recurves I always check my forms, I have some other ones with straps too.
Plywood warps, some of my pattern sanding templates warp also.