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My biggest issue is that this really just sounds like an SCP-ified version of The Mirror of Erised from Harry Potter. Do they have to see their own reflection, or just the mirror itself? Why a mirror, if it seems that what it shows people is not in the reflection, but in their own mind?
One of them commits suicide after he fails to integrate into his new life, and faces racial prejudice. His suicide note elaborates on how he hopes God will send him back to the "Heaven" he experienced.
This is such a huge turn from the rest of the concept. Suicide is a touchy topic, even here, and needs to be handled delicately, and the racial prejudice falls into the same category.
Overall, the theme of "the grass is greener" and "a comforting lie over an uncomfortable truth" are pretty well-trod (in general, not sure about on the wiki), and this doesn't do a whole lot with the concept that feels new or interesting. There are some potential story threads, but there's no real hook; nothing that gets me invested in the anomaly. Just your generic "your greatest wish but at a cost" tale.
Many SCPs take common tales of caution like this and do something new or otherwise subvert them - what do you plan to do to differentiate your story from the many others like it?