There are many teams that perform well against strong teams and perform poorly against less strong teams. Sometimes strong teams do not know the past analysis of weak teams and their players in detail so during training, the match situation goes against them due to not knowing the strengths of the opposing team players. If they were aware of other strong teams and their players in advance and practices their strategies to counter them in advance it would be easier to play against them. The same situation was seen in the case of Barcelona, they performed poorly against Rayo Vallecano. But despite being a weak team played very well because the Vallecano players were aware of Barca strengths and went to the field after studying the players of the opposing team.
In the case of Barcelona, they excel against attacking teams. They like it when a team comes out to play because they exploit the spaces the team leaves behind. This is why big teams are not always an issue for them. Small teams tend to defend more and play in a low block. When teams play like that, Barcelona struggles.
This season, Barcelona has not found their rhythm. When they do, they will play better. Their issues are fixable, and once they are fixed, they will get back to winning streaks. I think people are reading too much into the team's performance. It happened, they played 3 away matches in difficult stadiums, so it was expected. Let's see if they will improve after the international break when they return to the Camp Nou.