Aren't <br/><br/> html codes?
Just to make sure we're on the same page: I added the regex line under post-filters.
Are html codes within a regex working there too?
Yes and yes to both questions.
The plugin retrieves the webpage content in html format.
The
Letra de "..." com ... line appears like this along with the lyrics.

I can't say for sure but from previous tests, I think both "/n" and "<br>" usually match the same thing.
In some yml's, I've noticed the two being used interchangeably.
But just to be on the safe side, I always prefer using <br> as its the one that always appears when I inspect the source code of the webpage.
To get some clarity also, are you saying the Genius providers in v1.2.0.4 do not remove that line
or that the same regex I used in the post-filters section isn't working for you?