For example, AbstractGPUVecOrMat:

julia> LinearAlgebra.Adjoint{Float64, Matrix{Float64}} <: AbstractVecOrMat
true

julia> LinearAlgebra.Adjoint{Float64, CuMatrix{Float64}} <: GPUArrays.AbstractGPUVecOrMat
false

... because Adjoint is <: AbstractArray but not <: AbstractGPUArray. This is bad, because it breaks a bunch of generic code, e.g., JuliaLang/julia#53611 (comment).

I guess this is JuliaLang/julia#51910, however we probably need a different fix in the short term.