This applies to those with multiple drives in their computer and/or those who store files on remote drives.
If you wish Blocs to work properly, in particular to have proper thumbnails appear in Assets, the Blocs application, your Blocs document AND you assets (images, sound files, etc) MUST ALL BE ON THE SAME DRIVE.
Both my desktop and laptop have two or more drives in them across which I have organized my files and applications together with a robust backup system between computers and external drives. This works for every other application I use, but NOT with Blocs.
This is a security limitation of the WKwebview, a component that Blocs uses to generate the design canvas. It’s very likely no other apps you have installed use it.
Blocs does have a built in feature to get around the security limitation, however it can be tripped up by characters in path url that are not supported within a web development environment.
With all that said. Lots of improvements coming in Blocs 3.4 around assets and management. The beta for 3.4 will start next week and it’s pretty much all about improving the workflow of asset management.
It includes a new option to embed assets within projects to avoid situations were assets do not load when hosted across various storage areas.