SSH acting weird

[pibox]

I've experienced some weird SSH behavior. A scenraio that happend several times to me: The session suddenly freezes during some action (not sure what triggers it because it happened with different commands). I can't close the connection (no Ctrl+C or Ctrl+D). I stop the process SSH process (from the connecting machine). I try to connect again, I get prompted for a password, I insert the password, then freeze again.
So far I've solved this by physically reseting the server but this doesn't seem natural to me. Looking forward to your suggestions.

[WarheadsSE]

What device is this?
What medium is the rootfs?

[pibox]

Sorry, forgot to mention. This is a Raspberry Pi, and the boot medium is a class 10 SD card (I hope I understood correctly).