Forking a 2.0 notebook in tinker mode fails silently, then crashes page

Feedback
1

Steps:

  1. open a notebook that you have permission to edit
  2. open the history and select the latest version
  3. click the Tinker button
  4. make an edit
  5. click the Fork button

The spinner will animate indefinitely while the console reports two Minified React errors, #418 and #441. Eventually the page crashes and report a server error (and a code ERROR 1308055230 in my case).

Edit: #418 is always present and therefore unrelated.