If you suspect those plugins, or any plugins or theme, to cause the issue, then you should disable them, and try again.
If the problem is not solved with that, the issue would be on your server, since WordPress by itself shouldn’t have any issues updating, but it might be blocked or else disturbed in the process by (as you suspect) plugins or themes, or the server itself.
In the case disabling plugins and themes doesn’t help at all, you might want to check with the server host if they see some possible cause for this issue.
==> Remember to make a backup prior to updating, and prior to disabling plugins or themes.
==> You might be able to update by replacing the files of WordPress manually, this means, replace every file in your root folder unless the wp-config.php, the .htaccess file and the wp-content folder. You can get the “new” files from https://wordpress.org/download/
This is a risky process since you will be uploading files manually using a FTP service and thus a backup is even more important in this case.
Thank you! When I checked the backend process when reloading the upgrade page there is a 403 Error from /wp-admin/update-core.php?action=do-core-upgrade
Are you familiar with this scenario?
Basically the error means the server understood the request but refuses to authorize it.
So the first things to check is .htaccess file (you can simply delete it, and then resave the permalinks in Dashboard > Settings > Permalinks to regenerate it) and file permissions in general (for this you may want to get in touch with your hosting provider and ask if they somehow harden the server files/folders and thus could interfere with WordPress updates).
