I use anchors a lot and went to add one to a page that already had 4 on it. It inserted and linked fine, but when I updated the page, a different anchor disappeared. I have only been able to keep 3 anchors on my page at any time, and could not tell which anchor would get deleted when trying to add in new ones.
I went into the post code to add anchors using "name" and it saved just fine. Obviously a problem with your button.
p.s. please bring back custom color options, I have very specific colors for my brand that I use on a daily basis and no longer can with your update.