No idea. Maybe somebody who is not being banned can tell more on those assumption(s) ? Anybody ?
"I have not been banned, and I have neither used dubious IP addresses nor ordered any Nexperia parts from JLCPCB."
That didn't help much... Maybe someone can confirm that they
did order Nexperia parts and their order is being fulfilled. Conversely, the OP here had clearly stated that their most recent order before the ban announcement was about unpopulated PCBs and a stencil, i.e. no components at all.
I would very much expect that the Nexperia ban would be implemented by telling the customer "sorry, we can't sell you those components". Which would still be very annoying if it means an incomplete PCBA, or parts you already own being locked in stock at JLCPCB.
But it is very different from no longer serving a customer at all. The latter is much more likely prompted by something "suspicious" related to the customer himself -- like their location, the type of products or business they are involved with, or JLCPCB's lack of ability to assess one of these aspects. Using varying or untraceable IP addresses or email addresses still sounds like a plausible trigger to me.