Tactics study: the first plateau

I just finished my third round through the set of one-move tactics puzzles I use for training and get the strong feeling that I reached a plateau: At the beginning roughly 10 weeks ago, progress was fast, but now I barely notice any progress. If at all, it takes me slightly longer to solve the problems (probably because recently I spent more time working). I know that regardless of what you are training/studying for, performance is never going straight up. Therefore, I will go for the fourth round and also include working on some more complicated problems.