27?! That makes me with my onset at 13 feel quite mainstream. I've been told occasionally that it can't be PANS at that age. Well, somuch for that, evidently.
I think there is supposed to be a reason for it in that it's supposed to be a thing that happens when the immune system isn't fully developed yet, but perhaps yo u and I just have something odd about our immune systems. I mean, genetics can get you in all kinds of ways, so maybe we have some kind of as-yet-undiscovered genetic problem with our immune system that meant that whatever it was that's supposed to have happened by then that makes you no longer susceptible to PANS reactions, hadn't. Just speculation.
(It's also, I think, true that neurological Lyme disease is mostly not even about immune reacions but to do with the bacteris directly nib bling at neuron insulation, so presumably thed developed-immune-system thing wouldn't apply.)
(I am literally like a house with mice chewing the wiring. :-) )