Canadian companies alledgedly played large roles in the development of the F-117 and the B-2, so we potentially have knowledge of weaknesses unannounced to the world.
Russia/China have claimed multiple times that the frequencies they use on their tech defeat US stealth coatings, but personally I question their truthfulness.
The only time I am aware of US tech fighting a peer was the defence of Kosovo, and the Serbs had no trouble shooting down an F-117. In the current Iran war, the US seems to only do sorties with overwelming airpower, so we don't see stealth tech in action.