The second Tuchel was fired, Chelsea's team became disorganized. Chelsea was unable to find a solution to a host of issues brought on by a critical change they made since they believed that a new coach would be the key to winning the premier league or champions league trophy.
If Chelsea's owner had realized the money spent on bringing in two different coaches who didn't perform as planned to replace Tuchel, he might have chosen to give Tuchel more time to lead Chelsea rather than dismissing him abruptly after Chelsea's first champions league defeat of the season. Chelsea owner fervently believes that Chelsea will succeed if he signs his old-time friend coach "Potter" as Chelsea coach. That mistake alone caused problems for Chelsea's football club. They paid dearly for it by changing coaches in short intervals
Thomas Tuchel remained my favorite coach; I'm a Chelsea fan, and I was really delighted when he was appointed head coach of the London club; he led us to the UEFA Champions League in his first season in charge. Although he was fired by the new board of directors in charge of the team it was primarily because he was failing to achieve the club's expectations and leaving too much randomness for defeat. Chelsea is most likely a shambles right now, with the club rebuilding at the moment. Expect some substantially improved good outcomes from Chelsea next season.