The phrase "questionable reliability" means that there are doubts or uncertainties about how trustworthy or dependable something or someone is. Full definition
Looking deeper, though, what we should be asking is why satellites that could give us information critical to our survival are being launched on vehicles of questionable reliability. (realclimate.org)
During the launch of the Wii U, a debug menu of questionable reliability seemed to mention that a new Yoshi's Island game was destined for the Wii U. (snackbar-games.com)
Why this sedan is not neck and neck with the Camry and Accord in sales has a lot to do with Subaru's past history of questionable reliability, and the company's regional focus. (bestride.com)