I have noticed it as well, my bet would be it's got something to do with the combination of vasoconstriction and anxiety. Especially if the dose is quite high, towards the end it feels like I pulled the majority of the tendons in my body. It feels like become hard as steel wire, totally tensed up, while residual acid stimulation can resemble electricity running through you. A really shitty combination if you are exhausted from the trip itself. I was happy to discover relieving compounds at some point like benzo's or maybe GHB, etc.
It would seem strange to me if the variance this happens with were a random placebo or setting thing. Personally I can buy into the possibility of iso-LSD or lumi-LSD as degradation products vastly increasing the chance of these symptoms. I've heard a lot of protest against anything other than acid and the power on the mind it has being involved. I guess the mind in turn can have great power over the body but these would be awfully specific complaints. And moreover, what data is available on a lot of other ergotamine derivates and 'champagne LSD', the brown product everyone says to avoid... what do you guys think exactly it is you are risking with such champagne acid? I think it's a fitting theory that impure product can cause this very particular wired and painful feeling.