The problem is not avast but the site itself.
https://www.ssllabs.com/ssltest/analyze.html?d=online.bancaperlacasa.it&latest- This server's certificate is not trusted (expired 3! years ago)
- Still vulnerable to POODLE attack while a simple setting change is all that is need and already known for 2(!) years
- This server supports weak Diffie-Hellman (DH) key exchange parameters. Grade capped to B.
- The server does not support Forward Secrecy with the reference browsers.
If that is how the bank deals with security, I would not trust them with my money at all.