Last week, we where made aware that there is a bug in boards where you can relatively easily end up in a state where visualization blocks don't appear in the order that you expect, and reordering is no longer possible.
We have been working on a fix, and will roll it out as soon as it's tested & ready. When we do, there could be some additional changes to the board occurring the first time you try to reorder a board element in an affected board.
We will update you on this incident once the issue is resolved.