So that could be why I found these two site maps (see my very first post on this topic) which are not indexed for Google - so Google console says - because they have not to index instructions writen on it or something like it?

These two say (literately translated the best I can):

Excluded by a "noindex" tag. When Google try to index your page it found an instruction "noindex" and therefore has not included them. If not to index them was your intention, then perfect, else, take off said instruction. To know if such tag or directive its on a page, ask for in a browswer and look for "noindex" in the body answer and in the headers of the answer

Excluida por una etiqueta "noindex". Al intentar indexar la página, Google ha encontrado una directiva "noindex" y, por lo tanto, no la ha incluido en su índice. Si esa era tu intención, perfecto; si no, quita la directiva. Para saber si esta etiqueta o directiva está en una página, solicítala en un navegador y busca "noindex" en el cuerpo de respuesta y en los encabezados de respuesta. 

I have no idea what google issue could be. Sometimes i see all kind of strange and wrong data and warnings from google, for example responsive issues etc etc.

Thanks mate 🙂 I think I have taken all this thing way too seriously, was happier and less worried before 🤣 

Drives me crazy that my website keeps dessapearing from the very front page and I find not reason for it. By now I thought was sort of "safe" after been there by 5 days but once again has dissapeared from earth as before used to happens day yes day not

Thanks 🙂

My very main keyword mate, Foro de piano , I been showing up from some three weeks ago as follow: 

1st No where at all to be found, and I meant nowhere not even in page 20....

Then I were placed in the very first page 4th / 5th position for few minutes, never more than 20/30 minutes... and gone from everywhere again for days

Days after, again I showed in the very first page 4 / 5 position but gone again in say couple of hours and completely nowhere to be found anymore again

Days after, back again to the very first page, then stay there for a whole day and after that, once again lost from earth and nowhere to be found

Days after, back again to the very first page and from there on I stay on the first page today the whole day on, tomorrow the whole day lost, next day on, next day lost, and so on

And now finally I was in there permanently in 5th position of the 1st page for 4 whole days but yesterday I was gone again, then back again this morning, then gone a few hours later and by now I been many hours not even showing like I say anywhere. I run out of pages without finding myself at all 🤣 

For me your keyword (Foro de piano) is on the 1st page, at #6.