I think the problem with Rashford's drop in form is inconsistency and this problem can be see in more players in Manchester United team. The team is currently lacking team spirit and the atmosphere around the club needs to change because the kind of aura around is not motivating atall. This a team problem not just Rashford
Manchester United's problem is not just about one or two particular players as the root of the problem is the very erratic performance of the team. They have quality players, but they don't seem motivated to do well despite the fact that other teams may be much more likely to win match with improved form.
It's a matter of technique and strategy, maybe it would be true if someone who was tactically capable enough spoke about their problems then we would know where Manchester United went wrong last season.