Hello,
After mail services, it's FTP's turn to be secure in tlsv1.2
If you see a new certificate pop window to validate, validate it of course
In case of problems :
Restart FTP software
Filezilla, non-functional SSL problem because cached in the software :
http://blog.infusiontechsolutions.com/how-to-remove-saved-ssl-certificates-in-filezilla
If persistent, use unsecured simple FTP mode while waiting to find the solution
Thank you