、。
Earlier, for some reason, the mic wasn't on.
Literal
A-while-ago, what-kind-of reason [embedded-question-か], mic [subject-が] entered-not [polite-past-ませんでした].
マイクが入る is non-literal: 入る means 'to enter,' but with マイク it idiomatically means 'the microphone is on/picking up sound' — i.e. signal is 'entering' the system. どういうわけか ('for some reason') is a fixed expression: literally 'as for what kind of reason,' with か leaving the reason unspecified. The whole sentence is the speaker explaining a recent technical glitch.