Steps to reproduce:

1. Start the demo app with this example content that is comprised of 2 paragraph blocks, the second of which is empty:

<!-- wp:paragraph -->
<p>Hello</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph -->
<p></p>
<!-- /wp:paragraph -->

2. Place the caret at the second block, currently displaying its placeholder text ("Start writing...")
3. Hit "backspace" on the virtual keyboard. Observe that nothing happens. 💥
4. Hit "backspace" again. Observe that the merge of the blocks completes.