Opening – Book
The program comes with openings books that are optimally matched to the playing style of the chess engines.
If you have the impression that the program is playing odd, unpromising variations, this is due to the learning function for the book. "Learning" means that the engine independently changes the weighting in its openings book based on its experience in its own games. The learning function therefore only makes sense if the chess engine is playing with the optimal settings. If you, for example, play rated games with a low Elo specification, this has a negative effect on the preferences of the openings book.
If you take the following rule to heart, you can ensure that your openings book is not "made worse" by the different chess engines:
In the settings dialog for the openings book, set the option Learning strength to a low value when you play against the chess engines in Friend, sparring or rated mode. In combination with these "throttled" playing levels, the learning function makes no sense.
The learning function for the opening domain is very program-specific. What is good for engine X is not necessarily good for engine Y. If you frequently play with different engines, you should provide each engine with its own book.
Tip: When opening learning is switched off, the playing behaviour in the opening is significantly more varied. Especially with weakened playing levels this setting makes sense, because the program then also plays out a few less-good continuations.