RSS feed bizarre 500 Error: can't handle top level element 'html'

Hello,

For the past week, altfg.com’s feed has been having trouble reaching the IMDb’s reader/aggregator.

Yesterday, 20 posts went through. Today, only one went through.

I received an email from them saying that today they received the following error while trying to access altfg.com’s feed:

500 : can’t handle top level element ‘html’

I did several different Google searches, but couldn’t find anything about this. Does anyone have any idea what could be the trouble?

Here’s our feed:

https://www.altfg.com/blog/feed/

It shows up ok on Feedburner and has been validated via https://validator.w3.org.

I’ve contacted the hosting company. They said that our VPS server is clean. No 500 error messages logged today.

One thing: I noticed that when mod_cloudflare was activated on the server on Friday (the one before last), the feed started having problems. After it was deactivated on Saturday (two days ago), the feed resumed its “work” on Sunday (the aforementioned 20 posts).

However, I also noticed that cloudflare was still acting as a “DNS buffer” as late as Monday afternoon, when it was finally completely deactivated via its own control panel. I’m not sure if all this is related to the feed’s problems with the IMDb, but I thought I should mention it.

Any assistance would be *much* appreciated.