During implementing the video background support in the cover block, I found an issue. When I try to add a new block inside and I click on the "Add block" button, it removes the whole cover block. That happens only when the cover block is the only block in the editor and has at least two paragraphs in it. The first paragraph has content inside and the second is empty and is selected.

To Reproduce
Steps to reproduce the behavior:

1. Add the cover block and select an image as a background. (it has to be the only block)
2. Write something in the paragraph that is added and click return
3. The next paragraph should be added and selected.
4. When the empty paragraph is selected, click on the "Add block" button.
5. The whole cover block is removed and any other block can not be added.

Expected behavior
The block should be added to the cover block.

Screenshots

EDIT: I can reproduce it also for the group block.

Smartphone (please complete the following information):

• Device: Iphone 11
• OS: iOS 13.3