Previously indexed database missing much of its index
Massachusetts Births, 1841-1915, (https://www.familysearch.org/search/collection/1536925) was previously indexed more completely than it is now. Browsing, I find film no. 004341200, image 698 of 1036 which now indicates "No indexes are available" but I have a screen shot from a few years ago showing that this page was indexed for one of my relatives.
Any explanation? How can part of an index disappear?