So, the submarines are pressure vessels, and they have unifomral stress level in the wall.
It means the strength of the hull defined by the weakest part of it.
So, thez falsifyed report was about the cold temperature resistance of the hull material.
It means that if the Virginia has to surface to
1. due to emergency
2. to launch tomahawk
3. to communicate
Or during underwater arctic manouvre, it
1. hit bottom of an icesheet
2. has to float itself pressud against the icesheet above
then the part of the hull can be damaged due to the subparr quality, and that could destroy the whole ship.
It techincally needs only a small patch, but most likelly way more parts built from that material. The USA hasn't got too many suplier for submarine parts.
Most likelly one or two company shipping the steel.
This kind of issue doing nothing else, just restrict the Virgnias to get close to the Russian shores. Minor details : D
The operatinal change most likelly nothing else just a restriction of the affected boats to operate only in warm waters.
And again, the only reason why the USA havent got loss of life submarine accident is sheer luck.
That they haven't got in the manned space program, maybe that has less stringenth safety requirements and less rigous culture than with the submarines : )