Search ignoring certain text frames?

Hi

I have a book of daily meditations whose dates for each day are in anchored text frames. I need to do a search and replace on these, but Search ignores them. The main copy on each page is in a Primary Text Frame.

Even if I un-anchor the frames, Search still completely misses them.

I have removed all search parameters and am performing the most basic text search.

If anyone has any ideas about what might be happening here I'd be grateful, as I'm at a loss to explain why this most basic function should be behaving in this seemingly broken manner.

I've created a blank file with a Primary Text Frame on the Parent Page, and several text frames including a PTF on the page itself, and it is able to search in all text fields without any problems, but as soon as I anchor one of the text frames, Search is not able to search in all the text frames any longer, so either this is a bug or a bizarre design decision!

I'm on 16.4 on Windows 10.

Many thanks
Richard