Thanks. That makes sense.
I already did the workaround 1 from this article but didn't do the trick.
However, I did manage to speak with the developer of the plugin throwing the error message and he told me the CURL call he is doing in PHP code is relying in the WordPress bundle certificate. That certificate was expired so I downloaded the current version from WordPress, replaced it and IT IS WORKING now.
Thank's a lot for the help. Best regards