a false dawn
From Longman Dictionary of Contemporary Englisha false dawna false dawnHOPEsomething that seems positive or hopeful but really is not There was talk of share prices recovering, but that was just a false dawn. → dawnExamples from the Corpusa false dawn• That proved to be a false dawn, as Moravcik's replacement, McNamara, was the one who scored.• Tracers lit up the fog like a false dawn.• It was a false dawn, replaced soon after by a now starless night that was blacker than the previous hours.