Domain inconsistently working - 'Server IP address could not be found'

Recently, my site has stopped working consistently and is returning the error ‘Server IP address could not be found’.

The site name is https://socius-org.netlify.app/ or https://socius.org/

I’ve checked previous posts on the forum but they all seem to have much simpler solutions that don’t work in my circumstances.

You’ve deleted all the default records that Netlify added for you and added something that you were not supposed to. Remove it all (except the MX record). Then remove and re-add domain to your site.