Steps:

1. Create new Landing Page
2. Drag and drop two blocks, for example banner and embed
3. Configure these two blocks and Publish
4. Go to the edit mode of this landing Page

Alternative scenario:

1. Go to Page/site
2. Switch to Edit mode - block seems to be empty.

Actual result:

Both blocks seems to be empty, but when you go to the settings, fields have content. After publishing it works fine. It occurs only for the first time. It works like that in prod mode only. dev is fine.

Expected result:

Blocks' content should be visible all the time.