Let's Encrypt certificate works for web but stopped working for ftp and email

My Let's Encrypt certificate has as SAN property value:


I've assigned this certificate to my IIS website, my FTP server and as default SSL certificate in my mailing application "Mail Enable".
This always used to work. After a recent automatic renewal, somehow only my website still works, but when connecting via FileZilla to my FTP server I get:

	Status:	Resolving address of ftp.example.com
	Status:	Connecting to
	Status:	Connection established, waiting for welcome message...
	Response:	220 Microsoft FTP Service
	Command:	AUTH TLS
	Response:	431 Failed to setup secure session.
	Command:	AUTH SSL
	Response:	431 Failed to setup secure session.
	Error:	Could not connect to server

The exact same certificate is assigned to the FTP server as to the website:

Also, any mail I send out no longer arrives at my recipients.

How is it possible this certificate works for my website, but no longer for ftp and email? And remeber, it used to work, so it kinda has to be something with the certificate and not other settings. What steps can I take to resolve this?

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