expression
Expresses that something happens or is the case without a clear reason; often used when the speaker finds the situation puzzling or unexpected.
どういうわけか、今日は電車が空いている。
For some reason, the train is empty today.
どういうわけか、彼は急に怒り出した。
Somehow, he suddenly got angry.
なぜか also means 'for some reason' but is more casual and often used in spoken Japanese. どういうわけか is slightly more formal and emphasizes the speaker's puzzlement.
どうしてか is similar but can be used as a direct question ('why?'), while どういうわけか is typically a statement about an unexplained situation.
Phrase composed of どういう (what kind of) + わけ (reason) + か (question marker). The combination literally means 'what kind of reason is it?' and has become a fixed expression for 'somehow' or 'for some reason'.