Clear your site's cache and your web browser's cache

Thanks, but unfortunately, that did not work. I've even disabled the cache based on other discussions, but to no avail.

hmm ill check this out

Yep in the latest SVN version the design tab is not in the page defaults, but is in the rest of my pages...

I think I remember that Andrew wrote that this is by design for now. It's going to be there in the next version I think...

Does anyone know why some design has been lost, while other pages seem fine? It will be a pain to go through a 100+ page site to ensure that the CSS is OK.

I had a somewhat similar issue. The upgrade to 5.4 (from 5.3.3.1) stripped the styling from the blocks, but left the entries in the 'collectionversionblockstyles' table. When i tried to edit the blocks which had the styling, I got a whole bunch of errors relating to duplicate keys.

Deleting the rows from that table fixed the problem, but had to reapply the styles manually. I only had a handful of blocks to fix so not a massive deal but not ideal.

Since our sites are still in development, I'm going to switch most of our styling to custom templates rather than relying on the block design system. This will at least ensure a smooth conversion from 5.3.3.1 to 5.4.0