Open/Click stats on delivery

Hi,

I have a question regarding one of our transactional deliveries that I'm hoping anyone could t provide some guidance on.

We have several brands that all have the same transactional emails.

I was looking into the opens/clicks of some of our transactionals and noticed that only one of our deliveries has no open/click data when looking at the delivery (and seems to have never had this?) - though the data does show up in the reports section.

I looked at one of our deliveries where it works, and I can't find anything obvious or different between one that works and one that doesn't.

Appreciate the help