The SSH host key of the WiFi Pineapple is dynamically generated on first boot - after upgrading your device, you will receive a SSH host key mismatch when connecting via OpenSSH, Putty, or other SSH clients. This is normal when upgrading, and you should remove the offending key from your client and accept the new key (however, in any other circumstances you should not accept new SSH keys from a host unless you have confirmed they have changed!)