It seems like I can login from your backend now.

After checked further again, the reason why it didn't show any result is because you have set one of the category to 'Português' language, you can refer on my attached screenshot below.

How this search engine work is, first it will see your current user which language they browse, for example :

Someone trying to search this keyword "Download GeoPV" under this Português language e.g this URL https://youdomain.com/pt_br/forum/search/

It will show the correct result is because these thread is post in under this category 'GeoPV' as what you set this language to Português.

In other word, if you trying to search this keyword "Download GeoPV" again in English language page, it will not show any result.

By the way, based on what i checked on your current categories structure, it seems like your existing categories most of them also set to "All" language but only this category "GeoPV" you set to Português language.

Is it you would like these thread who posted in this category "GeoPV", only Portugues language can show these thread on the page?