Zpoints ranking list 'pollution'

The last couple of months I have been working on the ‘silly project’ of improving my Zpoints ranking to see how far up the ladder I could climb. Just for the heck of it, an older man trying to relive his younger days. With reasonable succes, where I was around position 4000 or so 6 months ago I found myself back at 171 last week. This week I was bumped back almost 100 places (my ranking is still the same though). I believe this is caused by a lot of B riders that suddenly appear if you filter on C. As an example take the cyclist with ID 325170. He was in cat C until a month or 2-3 ago where I have raced against him. At the time he won just about every C race that he entered and looking at his NP and the variability index he was clearly sandbagging. Then he got promoted to B - I believe - where he is still very competive with lots of top 10 and podium finishes. Good for him.
But now all of a sudden he is back at position 15 in the Zpoints ranking for C and if you look at his profile on Zwift power it says that his category is C (strange thing though is that there it says he is 1600th in the Zpoints list, which must be for the B category). What is going on here?
And this is just one example, there are many more riders in the Zpoints ranking list for C that have no ‘business’ being there.

James confirmed in the category update thread that there has been a recent change to the zFTP calculations; which has led to many instances of riders being downgraded a category.

Evidently by keeping track of your rank, you’ve been able to identify how many high ZP ranked riders have been moved from B to C as a result.