ASSERT error in CheckUnload.c

In my build of !12492 (closed), when running the test suite, I'm getting

Stderr  run  ( T4029 ):
ghc: internal error: ASSERTION FAILED: file rts/CheckUnload.c, line 460

    (GHC version 9.11.20240530 for x86_64_unknown_linux)
    Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug
Aborted

This happens for several tests:

• T4029
• MultiLayerModulesDefsGhci
• MultiLayerModulesDefsGhciReload
• MultiLayerModulesDefsGhciWithCore
• MultiLayerModulesNoCode
• T24471
• T7702

Something is wrong, but I don't know why it only affects me!

My UserSettings.hs contains this

-- | User-defined build flavours. See 'userFlavour' as an example.
userFlavours :: [Flavour]
userFlavours = [userFlavour] -- Add more build flavours if need be.

-- | This is an example user-defined build flavour. Feel free to modify it and
-- use by passing @--flavour=user@ from the command line.
userFlavour :: Flavour
-- Modify other settings here.
userFlavour = defaultFlavour
    { name = "user"

    -- No profiled libraries
    , libraryWays = Set.fromList <$>
                    mconcat
                    [ pure [vanilla]
                    , notStage0 ? platformSupportsSharedLibs ? pure [dynamic] ]

    -- Assertions on in stage1 only
    , ghcDebugAssertions = \s -> case s of
                                   Stage1 -> True
                                   _      -> False

    -- Everything built with the stage-1 compiler has -ticky, and -dcore-lint
    -- Notably, the libraries
    , extraArgs = defaultExtraArgs
             <> (builder Ghc ? (arg "-dcore-lint"))
             <> (builder Ghc ? stage1 ? arg "-ticky")
             <> (builder Ghc ? stage0 ? arg "-fomit-interface-pragmas")    -- Don't optimise stage0
    }