inexplicable
adj.adj. impossible to explain or understand. You use this when something happens and there is no clear reason why.
adj. unable to be explained, accounted for, or understood through logic or reason. Often used to describe sudden changes in behavior or mysterious events.
The car suddenly stopped for an inexplicable reason.
The team suffered an inexplicable loss despite being the heavy favorites to win the championship.
The detective was haunted by the inexplicable disappearance of the witness, as there were no signs of a struggle and the security cameras showed nothing unusual.
From Middle English inexplicable, from Middle French inexplicable, from Latin inexplicābilis, from in- (“not”) + explicābilis (“explicable”). By surface analysis, in- + explicable.
Often used predicatively after linking verbs like 'remain' or 'seem'.