Interference can also prevent two phones noticing each other when within 2m.
As a result, the Ada Lovelace study says, many matches would be missed while others would be recorded by mistake.
"Digital contact tracing will be less able to control for variables such as ventilation, direction of wind or environment, factors that are normally central to manual contact-tracing efforts," it says.
"[And] digital contact tracing will be vulnerable to all forms of fraud and abuse – from people using multiple devices, false reports of infection, to denial-of-service attacks by adversarial actors."
Nevertheless, researchers at the University of Oxford's Big Data Institute have previously suggested even if false and missed alerts were common, the spread of the virus would still be slowed and people would have to spend less time in quarantine.
An effective automated system should be quicker and more accurate than relying on human memory.
But since the app won't be 100% reliable or used by everyone, experts say manual contact tracing still has a role to play.
"If you ask me whether any Bluetooth contact-tracing system deployed or under development anywhere in the world is ready to replace manual contact tracing, I will say without qualification that the answer is no, not now and, even with the benefit of [artificial intelligence], not for the foreseeable future," blogged Jason Bay, who led development of Singapore's TraceTogether app.