Switches all of a sudden got an alert on its HTTP sensor stating: Error connecting with SSL. EOF was observed that violates the protocol

Have you checked that it is not a key length issue? New browser (and MS) security requirements enforce SSL certificates be a minimum 1024-bit key in length.

If you cannot configure/request the server need this minimum, consider the following workaround for bypassing on the client side: https://learn.microsoft.com/en-us/security-updates/securityadvisories/2012/2661254

From an admin command prompt, execute: certutil -setreg chain\minRSAPubKeyBitLength 512


Disclaimer:
The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.