It's hard to say whose problem it is, Chelsea's or the coach's... Lampard's return looks very bad, defeat after defeat and only one win. It's hard for me to say if it's the players in particular, it's probably the tactics of the coach who can't get the players on the pitch to play more confidently
Chelsea's problem is very complex, they are bad in every way. This may indeed be due to the coach being unable to provide a strategy that suits the players, and also the Chelsea players who seem to be less motivated and unable to apply the tactics provided optimally, or indeed their players are simply not competent. support so that Chelsea is currently in a bad point like this.
Even this crushing defeat against Man United actually closed Chelsea's career at the end of the season. They can't even qualify for the European League.