above all, the plot was still included in the development plan a few years ago.
That zoning areas are redrawn to cut out certain plots (typical application: brownfields of former businesses in town centers) or to reorganize them (typical application: follow-up of factual "border changes" between MI and WA areas) is already relatively rare. That zoning areas are redrawn to place individual parcels "offshore" is even more rare, and the (here of course only: relatively) most typical case will not please you: nature and emission protection concerns. You mentioned a GE, so it will probably be the latter here. Your plot was likely assigned to the buffer zone. In any case, the justification for the amendment can be copied 1:1 into your rejection letter.
Unfortunately, I cannot provide a development plan or a detailed land use plan, as I cannot find any. Why it was removed they could not or would not tell me.
Land use plans are uninteresting for political end users; a look inside is only worthwhile for those politically ambitious locally and conservationists. As a builder, you will gain no nectar from it. More interesting is the development plan, which itself – and likewise its amendment procedure – are public, albeit unfortunately not to be confused with information transparency (the backlog of digitalization in town halls is partially abysmal). It was not removed without reason; just because of the principle of appropriateness one does not do that just for fun. And there will have been a public display of the amendment procedure; if you were already a landowner back then, you would at least have been publicly involved. If a tabloid is simultaneously the official municipal gazette, you should not only read the obituaries. ;-)