Cannot edit block anymore

Nobody has claimed this yet.

### Search first

- [x] I searched and no similar issues were found

### What Happened?

I know this is not the most helpful report, but all of a sudden I cannot edit a part of my page anymore. It is all under one specific block. I cannot add new blocks inside that block, I cannot change indentation inside that block. When I remove a subblock by hitting backspace while the curser is at the beginning of the line, then I cannot add it back. Hitting Enter even removes the cursor from the page (seemingly).

### Reproduce the Bug

I have syncing on and edit the same pages on my phone. I think this block had a sign on it before telling me about a syncing issue, which I "resolved". That might have corrupted it.

### Expected Behavior

_No response_

### Screenshots

https://github.com/user-attachments/assets/b5e5193a-5dd5-4677-ba3f-5afcae873a82

### Files

_No response_

### Browser, Desktop or Mobile Platform Information

macOS desktop app (macOS 27)
iOS app (current iOS)

### Additional Context

_No response_

### Are you willing to submit a PR? If you know how to fix the bug.

- [ ] I'm willing to submit a PR (Thank you!)

No files, tests, or entry points are named. Start by reproducing the affected block with syncing enabled across the macOS desktop and iOS apps, including the listed editing actions. Done means the block again accepts nested blocks, indentation changes, deletion and restoration, and Enter without losing the cursor.

Written by the indexing model from the issue text.