What does the percentage next to the blocks/sec bar in the Crypto Storage mean?

That's the profitability of a currently mined coin.

The profitability works in a following way:

• Firstly, it is based on the coin you're currently mining, and it can be raised back to 100% by switching coins which are mined. It is building-agnostic, meaning that the profitability in current building does not affect the profitability in the next building.
• Secondly, after 1 hour of play, the profitability will fall to 50%, and the efficiency of selling and mining will change respectively. Once it falls to 50%, in order to return it back to 100%, you need to:
  • a) Leave the game and wait for 1,5 hour before it comes back up to 100%
  • b) Switch coins which are mined and sold everywhere, and wait for a period of 1,5 hour.