Enfold Child Not Saving

I’m finalising my wordpress website built with Enfold Child and suddenly any changes I make to the homepage are not being saved.

After I click ‘Update’, a little black box will appear as usual in the left bottom corner saying ‘Page updated. View page’, but in the menu bar on the top of the page, the cloud symbol still says ‘Saving’.

I’ve tried leaving it for more than 1 hr but nothing changes, and the only option I have is to reload the page or to return to the main menu, and then all changes are lost.

This only happens to the homepage, not for the other pages which are saving changes as usual.

There is no error message although I suspect it may have something to do with a site health issue which is flagged as critical: ‘Background updates are not working as expected.’

Below that it lists:

Error Some files are not writable by WordPress:
xmlrpc.php
wp-blog-header.php
readme.html
wp-signup.php
index.php
wp-cron.php
wp-config-sample.php
wp-login.php
wp-settings.php
license.txt
wp-mail.php
wp-links-opml.php
wp-load.php
wp-includes/class-wp-user-query.php
wp-includes/l10n.php
wp-includes/date.php
wp-includes/class-wp-oembed.php
wp-includes/images/w-logo-blue-white-bg.png
wp-includes/images/blank.gif
wp-includes/images/down_arrow.gif

Many thanks for your help and suggestions!