Looks similar to this other issue: playground-broken-after-update/751106
TLDR: delete the browser local storage for the playground site. (It will also delete the playground history, you can try backing it up if you need it)
Looks similar to this other issue: playground-broken-after-update/751106
TLDR: delete the browser local storage for the playground site. (It will also delete the playground history, you can try backing it up if you need it)