In the following situation, xxx is marked as unused, even though it is not:

Dep.hs:

module Dep (a, b) where

xxx :: Int
xxx = 3

a, b :: Int
(a, b) = (xxx, 1)

Main.hs:

module Main where

import Dep

main :: IO ()
main = print a

Minimal reproducible example:

 $ git clone --branch weeder-pattern-bug --single-branch https://github.com/amesgen/stuff
 $ cd stuff
 $ weeder --version
weeder version 2.3.0
hie version 9001
 $ cabal build
 $ weeder
app/Dep.hs:4: xxx

Also, b in Dep.hs is not marked as unused, but I am not sure if this is intentional.