[Python] I can't use dashed lines to draw 2 time series on seaborn

I face a strange problem with no answer found :

I want to represent this dataframe (which is a time series) :

ts_velo.head()

type_velo nombre
date
2016-09-01 VAE 0.980769
2016-09-01 Vélos 11.865385
2016-10-01 VAE 0.826087
2016-10-01 Vélos 9.152174
2016-11-01 VAE 0.711538
(...)


I can draw this graph :

sns.lineplot(x=ts_velo.index, y='nombre', data=ts_velo, hue='type_velo')




But I don't achieve to use dashed lines instead of solid lines.

I tried several things I read on stackoverflow, for example :

sns.lineplot(x=ts_velo.index, y='nombre', data=ts_velo,
hue='type_velo', dashes=[(2, 2), (2, 2)])

sns.lineplot(x=ts_velo.index, y='nombre', data=ts_velo,
hue='type_velo', dashes=True)

sns.lineplot(x=ts_velo.index, y='nombre', data=ts_velo,
hue='type_velo', dashes='--')


sns.lineplot(x=ts_velo.index, y='nombre', data=ts_velo,
hue='type_velo', ls='--')

g = sns.lineplot(x=ts_velo.index, y='nombre', data=ts_velo, hue='type_velo')
g.lines[0].set_linestyle("--")


But nothing works.

An idea of why I get this problem ?

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