Hi! I tried to create my own block plugin. Everything worked fine except the preview. The only thing it showed me was the block name and icon. After a while, I discovered the reason - my original block name was rating. I changed it to abc and suddenly the preview worked as expected. Then I renamed it to a-rating and it still worked. It seems the first character of the name have to be a letter from the start of alphabet.
I remember there used to be a similar problem with naming Editor plugins. Is it possible that this error somehow slipped into Blocks?