That clinches it. I had an ebot for RodS's reply on 4th June, but the remainder were un-notified as my hypothesis had predicted. I've seen the same behaviour in other forum threads.

I raised the problem here: What's really wrong with forum ebots but that was more than ten working days ago, so I'm not holding out much hope.

Sorry to interrupt - I realise you're discussing gallery ebots. I don't know if the two mechanisms are linked in some way.