I am playing a 100-card Brawl deck commanded by Zimone, Infinite Analyst, which contains 20+ X cost spells (cards where the mana cost includes {X}). My deck runs 38 lands, which should statistically produce opening hands of 3–4 lands on a regular basis. Instead, I am consistently receiving only 2-land opening hands and struggling to draw additional lands throughout the game.
I believe this is caused by Arena's hand-smoothing algorithm misclassifying X cost cards. Because the {X} variable resolves to zero when evaluated statically, the algorithm treats these cards as low-CMC spells. With 20+ cards being miscategorized this way, the algorithm calculates my deck's average CMC as artificially low and adjusts my opening hand to contain fewer lands than is appropriate — despite my actual intended casting costs for these spells ranging from 4 to 10+ mana.
This was previously reported (suggestion #40810486 — "Mulligan smoothing does not properly account for 'X' CMC cards") but that thread has since been archived, so I am submitting a new report. The issue appears to still be present and is particularly pronounced in Brawl format where X cost spells are more heavily featured in certain commander archetypes.
Steps to reproduce:

Build a Brawl deck with Zimone, Infinite Analyst as commander
Include 20 or more X cost spells in the deck
Run 38 lands
Play 10+ Bo1 games and track opening hand land counts

Expected result: Opening hands should average 3–4 lands given a 38-land, 100-card deck.
Actual result: Opening hands consistently contain only 2 lands. In-game land draws are also lower than statistically expected throughout the game.