It seems to survive when in solution with Cl ions all over, as is the case if it's in solution with HCl
Those are ions though. Basically reduced (as in addition of electrons) chlorine is Cl- ions. Chlorine is a very strong oxidant (all halogens are oxidative, some like chlorine are way more so than others, like I2, gaseous chlorine is oxidative enough to support combustion without the presence of oxygen). This means that elemental chlorine or Cl2 will oxidise things, becoming reduced itself. This action will can cause areas of organic molecules to become oxidised, in turn making then positively charged. Since the chlorine was reduced, it becomes negatively charged, so the chlorine attatches itself to the positively charged area of the organic molecule. As far as pseudo or meth goes, one of the places most succeptible to this is the benzene ring. Exposure to halogens will cause ring halogenation. Now some halogens aren't strong enough to do anything at all without some sort of catalyst, some will only react a little without catalyst, some don't need a catalyst at all.
Ions are already reduced, so a solution containing meth or pseudo that also has a plethora of Cl- ions will probably remain unaffected.
Post 508148 (https://www.thevespiary.org/talk/index.php?topic=7923.msg50814800#msg50814800)
(SHORTY: "Iodine from KI: This recently worked for me", Stimulants)