A few years ago I was trying to get get home on an early flight from an outstation (CLT I think) on a UAex carrier and the announcement was made that they were trying to find the plane and as soon as it was found we should be boarding shortly.
Approaching the podium with a "I really must not be awake enough yet... I thought I just heard you say the plane was missing" Gate agent told me that it had RONed in a hangar, someone had been sent to tow it over quite a while ago... the plane was no longer in the hangar, it wasn't at the gate but should have been by now, they we're "pretty sure" it was still somewhere at the airport but person sent to get it wasn't answering radio calls.
One of the more surreal conversations I've had [seems crazy to think that a jet, even a regional jet, could be "lost" -- but I guess at a busy enough airport...] but it did eventually show up about 30 minutes later.