false dawn
From Longman Dictionary of Contemporary Englishfalse dawnˌfalse ˈdawn noun [countable] formal DISAPPOINTEDa situation in which something good seems likely to happen, but it does not The ceasefire turned out to be another false dawn.Examples from the Corpusfalse dawn• The first quarter's sales figures were sort of a false dawn.• The global fund in all probability will prove to be another false dawn for the poor.