Blog post filters stopped working and there's an error

Hi, I'm working on a website for a friend and have now encountered an issue with blog functionality that I can't solve.

All the details:

I'm using BeHealthy

BeTheme -> options -> blog & portfolio -> blog -> options:

blog page is set correctly, load more: disabled, infinite scroll: disabled

I have created a blog page and used BeBuilder to set it up

On top of the page I used a BeBuilder element "filter form" to filter by category and by tags. Ajax input on change. Tags -> taxonomy -> field type switch. Categories -> taxonomy -> field type checkbox.

To display the posts I tried two options and neither works with the filters properly.

I tried going through settings -> reading. Then I switched that off and added a pre-built section Blog/Portfolio 02 in BeBuilder.

Whenever I try to use a filter, there is no reaction until I click "search" and when I actually click "search" I get sent to my homepage and the url is like website.pl/?mfn-advanced-filters-logic=AND&tax_post_tag%5B0%5D=4

The weird thing is, I think the tags used to work right after I first created them. I'm almost sure that I already tested them and it was all fine. I'm not 100% sure, though. Now that I got back to polishing all the details of the blog page, I realised they do not work at all.

Other issues I have:

I also can't figure out how to translate "search", "reset all" and "read more" into my language, even though the rest of the website is in my language.

What am I missing? I really need to overcome these issues. Please, share your insight.