@mikejolley.
I have now resolved this. It took me a little while to do it but with the help of my browser friend, F12. I managed to resolve all the H3 / H2 conflicts and the space that was added due to the extra class id added in the update.
I’m sorry that the Devs have been getting grief over this, not from me I hasten to add.
We all realise that change happens, the problem was that this part does not seem to have been listed in the changelog, though I may have missed this. There is mention of H2 for v 2.6.4 but nothing after that.
My issues were mainly look and positioning. The site works fine though I note a lot of users posting one star reviews on the plug ins page. This is not really helpful but I can understand the frustration if your upgrade has broken your site, especially if you sell things. ( I don’t currently sell ).
Fortunately for me only my staging broke. Though stress levels are on the up for scheduled live change!
If I can help anyone with the H2/3 side or the extra padding on the product image let me know. I might not be able to help but will give you my fourpence worth.
McP.