unreliable
un-re-li-a-ble
adjective
Not able to be trusted or depended upon; inconsistent in performance or accuracy.
"The old train service proved unreliable, causing delays."
Thesaurus
Synonyms: treacherous, dangerous, unsafe, irresponsible, undependable, fallible, temperamental, uncertain, erratic, unsound
Antonyms: dependable, reliable