I think there's a bug in cache invalidation, but my testcase isn't exposing it.
That got me digging into the implementation of ada-lang.c's symbol lookup cache.

It looks like nothing sets pspace_data->sym_cache.

Presumably, it should be set here.

static struct ada_symbol_cache *
ada_get_symbol_cache (struct program_space *pspace)
{
  struct ada_pspace_data *pspace_data = get_ada_pspace_data (pspace);
  struct ada_symbol_cache *sym_cache = pspace_data->sym_cache;

  if (sym_cache == NULL)
    {
      sym_cache = XCNEW (struct ada_symbol_cache);
      ada_init_symbol_cache (sym_cache);
    }

  return sym_cache;
}

Could be missing something though.