GarbaceCollection makes sense.
As I said, now it settled down a lot. My intuition tells me, that it's worse, the more people are online in the slack-channel. Maybe the more people are working on their scripts and regularly commit them to screeps, the harder the garbage collection hits. However, I don't have any statistics for this, just my intuition.
But as long as I have an explanation for what it could have been, I'm quite fine with it.