"already probably" is a very awkward construction. You might hear it in conversation as someone is trying to hedge their statement in the midst of actually saying it, but hopefully never in writing. "probably already" is a better word order if those two words are going to be strung together.
I will guess that it is not accepted because "maybe" is better translated as možná. If I'm wrong about this, one of the CZ natives on the team will correct me. :-)