BNFC release 2.8, and up to the latest commit.
The Java backend is sensitive to the order of the macros/productions.
For instance the following gives errors, both using CUP and ANTLR4:

separator Exp ",";
List . Something ::=  [Exp];
A . Exp ::= "a";
B . Exp ::= "b";

Instead

List . Something ::=  [Exp];
separator Exp ",";
A . Exp ::= "a";
B . Exp ::= "b";

seems to work fine.
I did not try all the other backends, but Haskell seems to work without problem with both formulations.