Uncommon, but difficult to fix bug on RSS FEED

Greetings WordPress Team,

After days and days trying to fix a difficult bug, asking even help on Hostgator Support Team, after that Hostgator Administrative Account Team, after that on Hostgator Linux Administrator Team, but even they could not find a solution for this bug and reccomend me to come here and ask for help to the developer.

My problem is that my RSS FEED is not showing. Its simply a blank page when i enter on RSS FEED Page.

RSS FEED on my blog worked properly and some day i see this error at my RSS BUTTON:

Unknown Feed – RSS Error: A feed could not be found at https://bestdownloaddvd.com/DownloadDVD/feed.

This problem come from nowhere about 2 weeks ago. Rss worked and i installed Rss Fixers Plugins after i saw the problem. I installed them separately, test them separately and none of them worked.

I reinstall wordpress and same error.
I even change the theme and same error again.
I deactivate every plugin..test after deactivation and same error.

At https://feedvalidator.org says:

line 1, column 0: XML parsing error: <unknown>:1:0: no element found

Feeds should not be served with the “text/html” media type

And at google webmaster tools says:

Empty Sitemap

Feeds should not be served with the “text/html” media type.

Its simply a bug that make RSS feed to dissapear without trace and i do not know how to implement it back.

I do not know what to do now.I hope i will find help here to resolve this issue. I loose a lot of visitors every day.

If any technical information about servers is required, Hostgator Team sayd that they can provide.

My website blog is: https://bestdownloaddvd.com/DownloadDVD

Best Regards