I noticed this efect first time about 3 seasons ago. During the game, the team is given a boost that lasts for about 10 minutes of game time. During that time attacking intensifies in great degree and it's not unusual to see 2-3 goals one after another. This does not seem to correlate with any actions of the manager, in fact I saw this happening without the manager present at all. Kinda happy hour.
Btw, I always laugh when I read about all these sophisticated tactics and formations and what should be countered with what... it might be all valid in real world, or perhaps in game like Football Manager, but this game, it appears, is much simpler than all that. The proof is simple: if you look at the ladder in your own league, you will find that it pretty much goes by the quality of the team, with everybody having different formation and not changing it for the whole season.