Hi,
I do also get a blank page with an error 500 HTTP response status on that page. My second paragraph was about this problem:
The 500 error on that BUD page can come from anything. We'll need the error message corresponding to that.
Please check the PHP error log of your server for the "fatal error" message corresponding to that 500 generic error.
If you don't know how to access your PHP error log, you might have to contact your hosting support as it can vary widely based on how the server is setup.
So please provide the fatal error message you can find in your PHP error log and we should be able to tell you what is the problem and what to do.
There is no minimum PHP memory required. However, the more elements you have to display on a page, and the more extensions you have installed on a website and the more it will require resources, including memory.