Hi there!
I have Gutenberg annoying error message “Updating failed. The response is not a valid JSON response.”, when I trying to add a lot content/fields inside one block.
The content page (Gutenberg json data) and the fields updating ok, even if I see the error.
For example, I have block with ACF flexible content items, ant I have 2 items inside and there is no error while updating the page:
https://screen.pictures/1592444010064.png
But if I want to add more fields/contents etc into flexible fields(Gutenberg json), I have error message:
https://screen.pictures/1592444170297.png
I have latest WP and ACF, php-fpm7.2 and NGINX
Refreshing permalinks not helps, SSL also configured correctly.
same problems was in Apache and many another different WordPress virtual hostings
thanks!
Problem solved with disabling html minification for json requests.
Hi Vitalii, thanks for sharing the solution – how did you disable html minification for json requests? Not sure if that was via a caching plugin you have, or some setting for ACF/Gutenberg. I have the same error message as you.