When I edit a page in page builder mode and try to reorder the blocks, sometimes the order is mixed up after saving. We did some debugging and found a way to reproduce this:

1. Create a Page with 3 blocks and publish it
2. Edit the page again
3. Drag the first block and drop it at the zone above it
4. No reordering is seen (but the state already changed)
5. Save the page
6. The First block is now at the second position

The cause is in the javascript, which does not check, if the nextBlock is the block being dragged (see Screenshot). See also attached video for more details regarding steps to reproduce.