On lichess.org, how are the ratings for the tactical puzzles computed? I am trying to understand how some puzzles I find challenging are as low as the 1400s, while others that seem obvious are at 2100+. As an example, consider this puzzle where the mate seems obvious (the white king has nowhere to go), so I would expect a rating in the 1200s, but the actual rating on the site (at the time of writing) is 2102.
4r3/8/p2p4/6k1/P7/1p2N2R/1P3r1R/K7 b - - 0 1
(Possibly a duplicate of "How are online tactic exercises ratings calculated?"? But I ask about the lichess.org puzzles specifically because the ratings there are so often surprising, especially for puzzles like the one above that have been played more than 30000 times.)