I have changed the database collation and the problem is still there.
Besides, I have restored the website with the appropiate database collation (utf8_unicode_ci) and there was any problem with special characters in the modules but I have installed the new version 3.4.3 again and now it doesn't display some characters.
Therefore, there's something wrong with 3.4.3 version of the module.
Could you check it please?
Thank you so much.