error when calculating ur

[tybug]

r = cg.Map(3079907, span='9', load=True)[0]
cg.ur(r)

(https://osu.ppy.sh/scores/osu/4017410581, in case the ranking changes)

errors with

Traceback (most recent call last):
  File "/Users/tybug/Desktop/Liam/coding/sandbox/__circleguard.py", line 6, in <module>
    cg.ur(r)
  File "/Users/tybug/Desktop/Liam/coding/osu/circlecore/circleguard/circleguard.py", line 212, in ur
    ur = Investigations.ur(replay, beatmap)
  File "/Users/tybug/Desktop/Liam/coding/osu/circlecore/circleguard/investigations.py", line 35, in ur
    hits = Investigations.hits(replay, beatmap)
  File "/Users/tybug/Desktop/Liam/coding/osu/circlecore/circleguard/investigations.py", line 268, in hits
    judgment = Investigations.judgments(replay, beatmap)
  File "/Users/tybug/Desktop/Liam/coding/osu/circlecore/circleguard/investigations.py", line 312, in judgments
    hitobjs = beatmap.hit_objects(easy=easy, hard_rock=hard_rock)
  File "/Users/tybug/Desktop/Liam/coding/osu/slider/slider/beatmap.py", line 1512, in hit_objects
    hit_objects = resolve_stacking_method(hit_objects, ar, cs)
  File "/Users/tybug/Desktop/Liam/coding/osu/slider/slider/beatmap.py", line 1618, in _resolve_stacking
    ob_n_end_position = ob_n.curve(1)
  File "/Users/tybug/Desktop/Liam/coding/osu/slider/slider/curve.py", line 173, in __call__
    ts = self._ts
  File "/Users/tybug/Desktop/Liam/coding/osu/slider/slider/utils.py", line 19, in __get__
    value = self._fget(instance)
  File "/Users/tybug/Desktop/Liam/coding/osu/slider/slider/curve.py", line 167, in _ts
    lengths[-1] - (length - self.req_length),
IndexError: list index out of range

I'm not convinced this is a slider issue yet because stacking on other replays (with the same mods, EZFL) resolves fine. Not sure how that's possible yet, needs investigation.