This fault was pointed out on one of the websites I managed, so I investigated.
All the usual tricks like updating everything and disabling plug-ins didn’t. So used the browser right-click – Inspect option to check for errors. By selecting the Console tab, I found the following error:
This article shows how to tackle this: https://wpti.ps/how-to-fix-bootstraps3-jquery-error/
This is ought to be a simple fix, but the files that need updating are part of the protected core files on the hosting that I use (AWS). Attempts to update the files use an FTRP client failed due to lack of permissions. Finally, I found this article: https://community.bitnami.com/t/permissions-wordpress-on-bitnami-aws/11883/9
I will reproduce the salient part as that’s quite important:
So i found a general catch all solution that seems to have worked for me.
People have been saying to change the owner of the files, but you can preempt the need to change the owner by editing the Apache configuration file at:
scroll down to the section just after the DSO module loadings and just after the PHP lines where it says:
(please note that I changed the normal <> tags to [ ] because of some sort of limitation in posting code here)
# If you wish httpd to run as a different user or group, you must run
# httpd as root initially and it will switch.
# User/Group: The name (or #number) of the user/group to run httpd as.
# It is usually good practice to create a dedicated user and group for
# running httpd, as with most system services.
Simply change User daemon to User bitnami and then run these commands:
/opt/bitnami/apache2/scripts/ctl.sh stop apache2
/opt/bitnami/apache2/scripts/ctl.sh start apache2
This did give me access to the protected area and I was able to replace the files with new versions.