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Could you post your site URL here, so I can have a look and try to leave a test comment?

If you want it to remain private, you can also contact us via this contact form:
https://jetpack.me/contact-support/

Here it is: https://www.sps.org.rs
As a matter of fact, I’m now receiving Apache2 start page as a response

I was able to reproduce the issue as well.

Could you let me know what other plugins are currently active on your site?

Akismet, Yoast SEO and Analytics, All in One WP Security, Envira gallery lite,
One click close comments, Visual form builder, Ultimate category excluder

Could you try to deactivate All in One WP Security, and One click close comments, and let me know if it helps?