How can we be sure?
"While they were still in disbelief because of their joy and amazement, He asked them, 'Do you have anything here to eat?' So they gave Him a piece of broiled fish, and He took it and ate it in front of them." Luke 24. 41-43
Can a religious experience be objectively verifiable? That depends on what one means by "religious experience" and the criteria one uses to verify it. The question is also begged, whether what has been so verified remains a "religious experience"? By their nature religious experiences are personal. For example, when Jesus took Peter, James and John up the mountain to witness his transfiguration, described in all 3 synoptic Gospels (Matthew 17:1–8, Mark 9:2–8, Luke 9:28–36), he told them not to tell anyone. For the time being anyway, that was to remain a religious experience, personal to them and to Jesus.
In contrast, Jesus seemed to be keen to establish his resurrection as different to a religious experience, though still unique. So he committed to an unmistakably physical act: eating. But did this change the nature of the experience of those who were present on the occasion - so that it was no longer so much a "religious experience" as an objectively verifiable event? Yes and no. Eating is a creaturely activity establishing that, in witnessing the risen Jesus so doing, they were not seeing a spirit because spirits cannot handle matter. On the other hand, the Bible records the sightings of the risen Jesus, though plentiful (over 500), as being restricted to "those who believed" (1 Corinthians 15.6), which suggests that seeing Jesus remains a "religious experience" - as real to those who experience it as anything objectively verifiable and much more meaningful, yet different.
Philosophy and psychology have the unnerving ability to undermine much of what we assume to be solid reality, re-presenting it as illusory. How can I prove to you that the computer I am writing this on is other than a figment of my imagination that happens to perform the function I expect of it (most of the time)? Reading this is probably enough to convince you but only because it conforms to your expectation, not because you are able (or inclined) to carry out the scientific tests which would establish its existence. Does that holds true for everything we come to trust and believe in? Is it real in so far as it works, or in so far as it makes better sense than other interpretations of what we are experiencing? Or is it because it reflects something/ someone behind/ above it all?