Why are the parameters of weibull not unique for a given data?

Question

I have a data which is the interval days of customers purchasing products. I try to estimate the shape and scale params by scipy.stat.weibull_min

But, the parameters returned from the fit function is not unique and when I try to constrain the scale param to be 1, it does not work.

Here is the three results with different ways for input:

shape, loc, scale = scipy.stats.weibull_min.fit(data,floc=1,scale=1)
#constrain scale to be 1  yellow curve
loc:1    shape:0.7318249351  scale:75.22852953

shape, loc, scale = scipy.stats.weibull_min.fit(data,floc=1, f0=1) 
#constrain shape to be 1  blue curve
loc:1    shape:1  scale:90.85

shape, loc, scale = scipy.stats.weibull_min.fit(data,floc=1)
#no constrain  green curve
loc:1    shape:0.7  scale:127.26

Besides, which curve best fit the original distribution?