Religious experiences are difficult phenomena for science, since they usually reach the boundaries of scientific capability. Without capability there is no hard evidence. Let me give an example of something that is very common, that is experienced by all, yet can't be fully proven by science. This is connected to limited capability.
If someone was having a dream, we can monitor the brain and brain waves and infer the dream state. If the person in the experiment was to awaken and tell us the specifics of their dream, there is no way to prove what they say is true, since there is no machine that can record all the specifics of the dream. A specific dream can not be proven, even if this phenonena happens billions of time each day and will all know it exists. Science would have to say, there is no hard proof for these details, therefore it does not exist based on any hard evidence we can generate.
The human mind is a frontier where the scientific method starts to break down. We only have some tools based on second person data collection, whereas the hard data would need to monitored from the inside; through the mind's eye.
If someone had a religious experience within the mind, like a semi-dream state, science can not prove it, even if it existed as common experience like a dream. If it was common enough, science might be able to hook the person to a machine and see how the brain activity is varying. It may infer something from that, but the specifics of the experience are out of reach. Therefore there is no data to prove this inner reality existed other than altered brain waves. It is not like the tools are there and there is no proof. Rather no tools means no proof. There is a difference but there is spin to make it appear the same.
The human mind is a final frontier but needs an upgraded science approach to address in a more objective way. Say we could induce a well trained scientist into a religious state, so he can observe the phenomena from the inside. His buddy's who trust him to be objective, will use the traditional second person tools for secondary data.
The inside scientist will use his conscious mind and training as the primary analytical tool, making note of all the details from his inside experience, that outside machines will miss. The inside person is the only scientist who would have anything rational to say based on direct data. The others can all pretend.
An analogy is trying to infer what is on the bottom of the ocean, while having science stay on the ship, at the surface of the ocean. We can use sonar and other ools, but these analytical limitation can not tell all the details. If it is not on the sonar, it is not there since it lacks proof.
To do it right, someone has to get into a diving bell to take a real look, and not just relay on limited surface machines. They would have to be able to use the diver as an analystic tool, with hope his training and power of observation is calibrate for objectivity. He reports the data he collective in his mind like a computer print-out.