The reason the referee stopped the play in the game of Panathinaikos - PAS Giannina.
The game was stopped by the referee Marios Labropoulos. Panathinaikos staff wanted to know why the official took that decision. The answer... was a banner on the stands, which can be found all over the internet.
The banner (photo below) raised on Gate 13 caused Labropoulos' decision to pause the game. The referee followed the rule and mentioned the incident in his official game report.