In Next syrup I suspect an incompatibility of Tolusyrup with ammoniacal anise solution

Not with Tolusyrup but with promethazineHCl is ammoniacal aniseed solution incompatible, which converts promethazineHCl into the water insoluble base. One might think of a suspension but still one will prefer a solution. In the latter case, one will have to acidifying. In the presence of Promethazine, one uses ascorbic acid for the sake of its antioxidant effect In favor of Promethazine. But also the ammonia will be converted into its ammonium salt. This could be considered unfavorable but finally the same conversion does not happen in the stomach either?