Sermon Series image not saving to series

Greetings,
I have just added a new image to a sermon series, but it is not persisting. The drag and drop is loading the image into the WP media file, but not sticking it to the sermon series itself.

I’ve tried both Chrome and Edge just in case it’s a browser thing, but it appears to be the same with both.

Curiously, I only needed to do this because I deleted 3 copies of the image from my media library (copies I thought were superfluous). I’m not sure how there ended up being 4 identical copies in my media library, but there were (the original and then -1, -2 and -3 suffixes). I wonder whether I tried four times before to get it to stick – which it did – but didn’t realise at the time that it was saving a new copy of the image each time…

Version 5.1.49