Thanks everyone for reporting that bug, we’re working on it.
Our current understanding of the issue:
When working on Google Sheets, an “unable to load file” prompt is displayed within the page. It prevents the user from working on his sheet and only a page reload fixes momentarily the issue, before the prompt comes again.
The prompt seems to be triggered by the autosave feature of Google Sheets but not on every autosave. Users reports working on sheets from 10 seconds to 2/3 minutes to 10 minutes, before the bug appears and the prompt is triggered. The delay is not constant between users and we’re not sure what determines the delay / triggers the bug
The stack-trace visible in the console brings us to… the spellchecker