For a query like this:

WITH
  abc AS (select 1 AS x),

  def AS (
    WITH
      abc AS (select 1 AS y)

    select * from abc
  )

select abc.x, def.y from abc, def

H2 in version 2.3.230 throws BadGrammarException because of the duplicate abc alias. H2 in version 2.2.224 does not, and accepts this query. The query seems to be correct by SQL standards.