Does Plesk only give you "Err 400 Time Out" or does it provide more text with that error message? If so, what is it?
Also, does Plesk have a verbose log somewhere you could provide? Because the information we have now is not much to work with, currently.
By the way, I can confirm your site is not accessible through IPv6. Its AAAA record is 2001:8d8:1800:8582::, but doesn't seem to be answering on port 80 nor port 443.