EXCLUSIVE: There’s nothing better than the positive unexpected at the summer box office, and we could have that in A24/Chern/Atomic Monster’s Backrooms which looks to do around $20M when it opens in the post Memorial Day corridor of May 29-31. The movie, which literally just finished post-production, arrived on tracking this morning. Should those projections hold, that’s a great result for a movie which cost under $10M (financed by Chernin), and one which is opening in the wake of Lucasfilm/Disney’s Star Wars: Mandalorian and Grogu s without any PLF or Imax screens. The sense with Backrooms is that there’s a stickiness around it with the under 25 set who are rabid fans of the Kane Pixels created IP from 2019. The IP launched on 4chan, spread on Reddit and fan wikis, and inspired games on Roblox and Minecraft.…