The iter-n and iter-n-sep patterns in SDF cannot be imploded by implode-asfix.
Consider the following definition niter-test.sdf :
----
module niter-test
exports
  sorts Foo Bar

lexical syntax
    [\ \t\13\n] -> LAYOUT
    "foo" -> Foo

context-free syntax
    "(" {Foo ","}2+ ")" -> Bar {cons("TwoOrMore")}
    "(" {Foo ","}+ ")" -> Bar {cons("OneOrMore")}

context-free restrictions
    LAYOUT? -/- [\ \t\13\n]

context-free priorities
    "(" {Foo ","}2+ ")" -> Bar
  > "(" {Foo ","}+ ")" -> Bar
----

and an example file: test.nit
----
(foo, foo)
----

packing and table-generation goes fine, but when running
$ sglri -i test.nit -p niter-test.tbl | pp-aterm
or
$ sglr -i test.nit -p niter-test.tbl -2 | implode-asfix |
pp-aterm

the following output is produced:
----
TwoOrMore(
  appl(
    prod(
      [ cf(sort("Foo"))
      , cf(opt(layout))
      , lit(",")
      , cf(opt(layout))
      , cf(iter-sep(sort("Foo"), lit(",")))
      ]
    , cf(iter-sep-n(sort("Foo"), lit(","), 2))
    , no-attrs
    )
  , ["foo", None, lit(","), Some(" "), ["foo"]]
  )
)
----

When the 2+ production is left out, all parsing into the 'OneOrMore' constructor goes just fine. I also tried an 1+ pattern, but this is desugared into a normal + in some earlier stage.
And, as said: the above also fails for the iter-n (w/o separator)