John of you lost inches in your neck and you could still breath in the suit before I'm betting your seal is too loose on you your neck seal will span an inch or so from one neck to another without a different cut being required but I doubt it would span inches. I lost weight and went from a 18 1/2 neck to a 15 1/2 and definitely required not only a new neck seal but a new suit
my bet is its time to change the neck seal.
Have fun try to stay dry its frustrating diving a semi dry suit One of my suits has wrist issues when I'm working my tendon really breaks the seal and then I get soaked up the arm.
I think I went from from a 16.5 or 17" neck to a 16" neck...so not that much. However, if combined with the neck seal stretching...might be enough to cause leaking.
What surprised me was that it happened on two dives in a row. Yeah...semi-dry when you are expecting dry is no fun.
Thanks;
John