Website & WP Dashboard crashing randomly

Hello.

I build and maintain the website Sevilla Studios, at realmofsevilla.com

I am experiencing several issues with my WordPress website and have been unable to solve the errors. My website has been working perfectly for the last few weeks, but at some time early yesterday, I began running into errors both on the front-end and back-end of WordPress. While clicking between pages both on the website and in the WordPress dashboard, the website will randomly crash sometimes and display either an ERR_CONNECTION_CLOSED or a bad 504 gateway, but sometimes other errors occur as well. It doesn’t happen every time and seems completely random. In addition to this, the website is now loading extremely slow and I have a lot of trouble trying to change any settings or do anything in the WordPress dashboard. I used Jetpack to run diagnostics on site health and everything seems fine. I also tried disabling several plug-ins that aren’t essential to the website’s functionality, but again it did not resolve everything. I am very confused about why this has happened as I did not change or update anything before this problem began occurring. If anyone has any advice or may know how to resolve this problem, it would be greatly appreciated. Thank you.

The page I need help with: [log in to see the link]