#1 Unclear Role
Let's follow the timeline of Coutinho at Barcelona. He joined in the window of January when Dembele was injured. Hence, he was slotted into the first team as a left winger. At the left wing, his lack of serious pace and muscle made it difficult to thrive in those areas. It was apparent that he can't work as a winger for Barcelona as defenders with some pace and/ or muscle dealt with him with ease. When finally moved into midfield, he faced some serious competition from the likes of Arturo Vidal and Arthur.
However, even when played in midfield, he ended up taking higher position than it should be, due to his high attacking instincts and low defensive tendency. Albeit, given the lack of proper winger characteristics, he always ended up playing as a 'Hybrid Winger'.
Whenever Coutinho plays as a hybrid winger, he is unable to engineer much for his partners. Though, he is no stranger to playing in midfield as a creator, his roles at Liverpool were mostly positioned a bit higher up the pitch. It was more of a number 10 position. However, at Barcelona, playing alongside Lionel Messi who occupies that same space means that, there is no room for another player. Also, Coutinho almost always operates in the left half space, regardless of his “official” position, which complicates his situation.
During his spell at Anfield with Liverpool, he was predominately used as a central attacking midfielder. The fact that the opposition teams didn't sit back against Liverpool then, as they do with Barcelona in La Liga, also helped him. His role was to pull strings and provide defence splitting passes. However, the Barcelona version of him mostly makes square passes and runs into the box. Maybe the pressure to perform has overburdened him. He isn't much involved in playmaking these days and mostly attempts for goals, that too with poor decision making.
Perhaps a new formation with a more defined role could bring the best out of him. Or maybe he has still not understood the 'Barca DNA'. Whatever the reason is, one thing is certain, time is running out and Coutinho needs to switch on reall soon or......