Users on a WordPress.com Business plan have reported encountering the following error when attempting to publish posts and pages through Calypso:
Updating failed. The response is not a valid JSON response.
As the original Happiness Engineer who reported the issue explained:
In this case, the post/page edits are not saved in a revision, and the changes must be copied/pasted manually in order to be saved.
This issue seems to occur when a user starts working on a post or page, and then steps away for a period of time. The issue doesn’t seem to be readily reproducible, so it’s tricky to troubleshoot.
This issue has been reported here too: Updating failed. Error message: The response is not a valid JSON response – Centos 7 · Issue #18783 · WordPress/gutenberg.
This issue is for added visibility, as suggested here: p1585558290023800-slack-C02FMH4G8 (the link to the expanded, internal report is in that discussion thread).
Context / Source
Multiple user reports over the course of several months.