[Kindle] Problems with cover and title.

Hi,

I'm sorry if I write the same thread already written in another section, but I don't know how to delete the previous one, in the Amazon Kindle section, and I think this section is more suitable for my problem.

I'm having trouble viewing my ebooks, treated with Calibre, and sent to my Kindle Paperwhite 2019.
In the beginning I passed all my books in .mobi or .azw3 format and they were displayed perfectly, with the title in the format I chose and with the cover. Then suddenly, after doing a synchronization of my Kindle, but I don't know how influential this operation can be with the problems that arose.

The first problem was not to display the covers on Kindle home, both for the .mobi and for the .azw3 format.
I solved this problem, but only for .mobi files by selecting the "Enable sharing of book via facebook ..." item in the "preferences -> output options -> mobi output" section, activating the same option in "azw3 output" for however the .azw3 format does not change anything.

The second problem instead concerns the title of the books displayed on the Kindle, before everything worked well, now no longer.
For the .azw3 format everything ok, I set in preferences in "metadata plugboards"
azw3: KINDLE2 = ([{pubdate} • {series: ||:} {title}] -> title})
While for the .mobi format I see only the title of the book even if in "metadata plugboards" I have set
mobi: KINDLE2 = ([{pubdate} • {series: ||:} {title}] -> title})

By unchecking the "Enable sharing of book via facebook ..." item in the "preferences -> output options -> mobi output" section in the .mobi format I do not see the covers nor the title of the book in the format I would like.

Thank you so much for future answers.