Because I’ve got “Block third-party cookies” enabled by default, it seems to block access to localStorage
I’ve opened an issue at codesandbox-client and a quick browse through the code, it looks like there is a unused InMemoryStore that it could fall back to in this case.
Probably any online editor will fail to work without cookies enabled for their site. Not sure what can be done though. Will it work by just enabling InMemoryStore?
I didn’t realise that blocking third-party cookies also blocked third party localStorage access, but it looks like that is where all the errors are coming from.