Charles,
Regarding PWB that appears to be less stiff, let me offer the following:

Stiffness increases with the cube of the thickness, so check the PWB to make
sure that you are getting the same dielectric thickness and also copper
thickness.
Assuming the thickness check is OK, have your supplier give you the glass
fabric construction for the laminate used in the PWB  and  look at the glass
to resin ratio.  High volumes of glass will give stiffer products and thick,
heavier glass fabrics like 7628 are preferred over 108 fabrics.  It is
possible your PWB supplier changed his laminate sources and for the same .062
thickness laminate this new supplier uses a different glass fabric
construction than the old supplier.

Regards,
Lyle Wallig

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