They updated the code for the Steem blockchain. They didn't do a good job testing it. From what I hear they just write the code, but make the witnesses validate it. And it seems the witnesses didn't know there was a test server to try it out.

Rather than having bandwidth like we did before, they're using "resource credits" to measure how much we can interact with the blockchain. They didn't set the level of credits that everyone got high enough.

Mana and resource credits are the same thing as far as I know.