Just in case somebody else comes across this:
I had the same problem, domain shows other domain in the same server. Both where on Cloudflare, with Cloudflare SSL
When SSL was set to 'flexible' it worked fine, but with 'full' or 'full(strict)' the wrong site was shown.
I changed then from Cloudflare SSL to Letsencrypt SSL and set the SSL in Cloudflare to 'full(strict)' . No errors after that.