Oh dear, they seem to have done some tidying and removed index entries for records where the images haven't yet been digitised, for example deaths before 1879 and marriages before 1864.
Just tested a number of pre 1879 deaths, where previously the index would return the death, but have no group registration id number as there wasn't yet an image to view. Now, the index entry is awol.
Maybe someone else would care to check that I haven't just imagined this.