Grammar compiles after adding docstrings but ACE assert fails

I’ve added some docstrings (a lot) to my grammar, and the grammar compiles but when I try to run ACE on anything at all, I get:

ace: type.c:625: type_to_string: Assertion `ty->name[0]=='"'' failed.

What did I likely do wrong? I tested things with one docstring, with and without whitespace preceding the opening “”", and things work. Before I start binary search, anyone knows what sort of thing can be the culprit?

The culprit is this code which has nothing to do with docstrings but I carelessly uncommented it along the way:

;n_-_mc_ge := n_-_mc_le &
;[ STEM < "n_-_mc_le" >,
;  SYNSEM.LKEYS.KEYREL.PRED "_generic_n_rel",
;  TRAITS generic_token_list ].

The way it implements TRAITS is probably wrong, with respect to the SRG.