I had the same issue but this was being caused by another plugin : Kwayy html sitemap
After deactivating it worked fine
(I say fine, there are php notices all over the place)
In WP preg_replace is deprecated, like the warning says.
It should be preg_replace_callback().
Plugin developers have been having this issue for at least 2 years, from what I understand preg_replace should not be used because it causes issues on certain hosts.
I don’t have a site to share with you at the moment, but I’m using the latest version of WP.