Coincidentally the first reduction came with a change of power from the SPD/Greens coalition to the CDU/FDP and the second slump when the energy and business ministry went from the SPD in the coalition to Peter Altmaier of the CDU.
In a recent debate on energy in parliament the current chancellor from the SPD (labor equivalent) responded to criticism from the CDU (conservatives), that the current government is fixing the huge mess left over by the previous governments (lead by the CDU). I'm not a big fan of Olaf Scholz (the current chancellor) in general, but rarely was there a truer statement.