I have to say that I also, like GLC, have absolutely no memory nor cognitive problems while in POIS, so this leads me to think that memory dysfunction is not part of the center, essential cause of POIS, even if present in most 'sub-types" of POIS. Or, from another point of view, POIS may includes more than one specific syndrome, and those different sub-types of POIS could have different physiopathologies, even if very similar in clinical presentation.
When I have found this forum, I have noticed that it was kind of usual here to put cognitive symptoms in the same basket with emotional symptoms like anxiety, social withdrawal, depressive feelings, mood swings and the like. Since in my case, emotional symptoms were very severe, and I never had any cognitive symptoms, I came up with the symptoms clusters I have proposed last year, making these two categories of symptoms into separate clusters. For me, it is clear that the cognitive symptoms are not produced through the exact same metabolic way than the emotional symptoms (in my current view, cognitive symptoms comes from kynurenic acid toxicity in the brain, and the emotional symptoms from quinolinic acid toxicity, but being toxic products of the tryptophan metabolism hacking toward the kynurenine pathways ).
Just like you, GLC, I have all my mental accuracy and memory while in POIS. It is only the fatigue or the lack of motivation or other emotional symptoms like anxiety that hinder my intellectual performance. Hopefully, that has been very rare, so I could have been highly successful in university, and after in my pharmacy career and as a business owner. When I read about many POIS sufferers being unable to go on with their studies, I realize that at least, POIS didn't have that consequence for me.
Relative to chronic memory problems that are worsen in POIS, but still present when not in POIS, like Defsync describes, I think there is some other chronic problem, apart form POIS, causing the chronic memory problems, and POIS just makes it even more worst for a week or so. My take on all POIS brain symptoms, be it cognitive or emotional, is that they are related to an acute encephalitis state ( which means a state of inflammation in the brain). If you look up the symptoms of a mild encephalitis state, they sure look like POIS symptoms.
Defsync mentions specific memory problems after alcohol consumption. It is well known that alcohol is toxic for the brain, so this causes inflammation and worsen the brain dysfunctions. Memory loss, lack of coordination, judgment impairment, personality change, are all known effects of alcohol, mediated by acute, temporary brain toxicity. I believe POIS, through another pattern, creates the same kind of acute, temporary inflammation in the brain, manifesting in cognitive or emotional symptoms, or both, depending of personal vulnerabilities.
Of course, POIS causes more than "just" brain-related symptoms ( and that is why there are 4 clusters of symptoms in my classification of POIS symptoms, not just 2 ).