RSS feed encoding problems after php upgrade

I upgraded to php 7.1 and then added the cpanel nginx plugin. I even tried burning the feed with feedburner but output was the same.

If you look on the bottom right of the site https://nonsmokersclub.com, rss looks like:

Κάπνισμα σε μονάδα υγείας Β��ωνα, Ρο�μελης 7