When Lugo starts running to start the fight with Nassir, you can see Agron behind him as he runs in front of Spartacus. In the next shot, Agron is next to Spartacus and throws a cup of wine at him as he passes again in front of them.
Varinius is incorrect when he tells Glaber he is not bound by the Senate's decision for him to return to Rome. At that period of Rome's history there were 8 praetors subordinate to the two lead magistrates, the Consuls. Praetors held imperium (the power to lead an army) but only if a Consular army was not available or required (Rome's initial response to the uprising was to underestimate the force required) The Senate would have voted the army to Glaber's authority they could (and regularly did) remove that authority if they wished.
Illithya says that she does not remember in which direction they traveled when Gannicus captured her and took her to the camp. Yet after Spartacus released her, she was able to walk back to the villa in Capua.