Getting 500 Server error

Hi, I seem to be having some sort of a server issue. I'm getting a 500 server error when trying to save a post. It does seem to save it, but every time it sends me to a blank page with the error. The one exception to this was the last time I tried and it gave me this error.

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 1720320 bytes) in /home/admin/public_html/wp-content/plugins/wpmu-dev-seo/includes/external/simple_html_dom.php on line 1628

Additionally I use Elementor as my visual builder and when I try to save with it I also get the 500 error.

I have granted support access to allow the experts to take a look if needed.

Thanks!