Barcelona have become an unstoppable team at the start of this season's La Liga as they have won matches against all teams from the start. There is a difference between their early performance and current performance this La Liga season as you mentioned. One reason for the change in their performance could be player injuries. From the beginning these team players had no injuries but currently some special players in their team are injured due to which their team performance is not good. The match in which Barcelona drew against Real Betis yesterday was completely unexpected.
Barcelona had a great opportunity to increase the gap with Real Madrid and increase their chances of maintaining their top position. However, Barcelona unexpectedly failed to do so. The first half of the match looked like Barcelona would win the match easily, but the final result was completely different. Both teams performed well in the match. Although Barcelona is ahead in terms of possession, they are behind Real Betis in terms of attack.
There is a big difference between Barcelona at the beginning of the season and Barcelona today. This may be due to the injuries of some of their key players. However, I think the injuries of the players are just an excuse. The coach must plan with the current players in his team and create unity among them.