Reddit shuts down viral thread on the existence of nuclear weapons

CORRECTION: Thread still open but I'm blocked from discussion.

I posted the following question to reddit r/askscience:

The random-walk model of nuclear chain reactions shows that the critical mass of uranium-235 for a nuclear weapon is 13 tons. What is the flaw in this model?

Hiroshima was reportedly attacked using a nuclear weapon based on highly-enriched uranium-235. The explosive material in the bomb reportedly had a mass of 64 kg. However, the random-walk model of nuclear chain reactions led Werner Heisenberg to believe that a nuclear weapon with that strength would require 13 tons of uranium-235. What is the flaw in the random walk model of nuclear chain reactions, if any?

The question was viewed 160 K times before the post was removed. No explanation was given for its removal. A captured version of the post is here. An archived version of the thread is here.

UPDATE: reinstated as of 9:46 PM EST 01/06 at https://www.reddit.com/r/askscience/comments/1hvainh/comment/m5t5jjn/?context=3

Although I am locked out of commenting section.

UPDATE: Jan. 11, 2024

Banned from r/askscience - see message from reddit in response to submitting question to r/askscience forum. No explanation given for banning.