Why is the second season so much more difficult?

In my first season at managing in the A-League, I finished first in the table, progressed to the series grand finals and won the whole thing. I lost about 9 games in total but my team was awesome! So far in my second season, my team cannot stop losing. The core of my team is the same as the previous season with a few additional players that are big improvements to the squad. I started off using the same tactics that proved to be so successful in my first season but results straight away went against me (this included losing to teams at the bottom of the table). I have tried changing my tactics, configured my training schedule and rotated my players and yet I seem to lose the majority of my games. What makes this even more frustrating is that my players are performing really well with high averages. So many matches have been played where my team is absolutely battering the opposition and yet I end up losing even if I'm a couple of goals in front.

I just don't understand how in my first season I can be champions and in my second, I am languishing at the bottom despite individual/team performances being so good. Has anyone else experienced this type of problem? Is this just the dreaded second season syndrome?

This normally happens for one of a small set of possible reasons, the most common being the one I'll indicate first:

(1) People tend to buy a 'glut' of players sometimes after the first season without realising that it might take a while for them to settle into the team, if you do this try to bear in mind that initially a cameo appearance for some of them might be best - if you change 5-6 of your first team players at the same time then you're almost asking for a side to underperform slightly as they're not going to play as a team initially until they get to know each other.

(2) Players aging, sometimes a critical player might 'cut it' in the first season but have lost a little pace or ability by the time the second season rolls around.

(3) Promotion, your star player in a lower league might only be a 'competant' player in the division above - I find this with Brighton in the game generally, I can 'cruise' my first season and go up - but the Championship is a whole new kettle of fish.

It could be a combination of one and two I guess. I did buy new players and started to introduce them gradually but they seemed to be performing so well that I slotted them in the first team after about four games. A couple of my key players from the previous season are around the 30 mark so I guess aging could be a factor. I just didn't realise it could have such an effect on the team.