Hi, After some connection issues, I found that some website's TLS certificates are incompatible with the Wifi 101 shield.
Check the website you are trying to connect to by using the following TLS certificate website: https://www.ssllabs.com/ssltest/index.html
Examine the certificates and check they do not use SHA384 or higher hashing cyphers; the Atmel ATECC508A Cryptographic Co-processors maximum hashing is 256bits (SHA256): http://www.atmel.com/images/atmel-8923s-cryptoauth-atecc508a-datasheet-summary.pdf
So: RSA 2048 bits (e 65537) / SHA1withRSA >>> OK RSA 2048 bits (e 65537) / SHA256withRSA >>> OK
RSA 2048 bits (e 65537) / SHA384withRSA >>>> Not OK ... etc ...
All the certificates are hashed during the TLS handshake so they all have to be 128 or 256 only!