Yes, it might be unintentional, but it can no more be coincidences because I have observed this 3 times so far. The bad period starts after the construction is started and ends after the construction is complete, be it a 16-day construction or a 3-day construction. When I observe my team playing during these bad periods, it seems that my team is being 'blocked'. After a construction is complete, I can clearly see the 'release', and my team performs as it should again, winning convincingly against teams of lower quality.
I have put a thread concerning this in the bugs section, but no improvement so far.