There are two types of penalties (which might be the wrong word for it), based on team size imbalance and number of players in the match.
If one team has 3 extra players they will get their earn rate reduced from around 10 Credits per minute to 7, for as long as that imbalance occurs. If a server only has 2 players in it the roughly 10 Credits per minute rate would be reduced to something like 2 or 3, for as long as the server has very small numbers.
The point of these systems is to help prevent farming by people stacking for bonuses or trying to farm wins on small servers. In most cases quick match should be ensuring servers are filled quite quickly and balancing the number of players, to minimise the penalties, but that is still being balanced.
Once we get to fixing the scoreboard I’m sure we can represent these much better on it, right now I can totally understand while they feel confusing.