Issue 1:
Bug report

Bug summary

When plotting scatter data with symlog y axis, the data in the linear part are not plotted

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(0,1, 1000)
y = (np.random.random((len(x),))-0.5)*100
c = (np.random.random((len(x),))-0.5)*10
plt.scatter(x,y,c=c,marker='o',lw=0)
plt.yscale('symlog',linthreshy=10)
plt.show()

Actual outcome

Matplotlib version

Operating system:

Matplotlib version: 3.1.0

Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg

Python version: 3.7

installed via conda, default channel

Issue 2:
Bug report

Bug summary

Since I updated to 3.1.0, symlog looses some points, at least when drawing a scatter plot

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np

x = [1.0000e+00, 2.0000e+00, 3.0000e+00, 4.0000e+00, 5.0000e+00, 6.0000e+00, 7.0000e+00, 8.0000e+00, 9.0000e+00, 1.0000e+01, 1.1000e+01, 1.2000e+01, 1.3000e+01, 1.4000e+01, 1.5000e+01, 1.6000e+01, 1.7000e+01, 1.8000e+01, 1.9000e+01, 2.0000e+01, 2.1000e+01, 2.2000e+01, 2.3000e+01, 2.4000e+01, 2.5000e+01, 2.6000e+01, 2.7000e+01, 2.8000e+01, 2.9000e+01, 3.0000e+01, 3.1000e+01, 3.2000e+01, 3.3000e+01, 3.5000e+01, 3.7000e+01, 3.8000e+01, 3.9000e+01, 4.0000e+01, 4.2000e+01, 4.3000e+01, 4.5000e+01, 4.6000e+01, 4.8000e+01, 5.0000e+01, 5.2000e+01, 5.5000e+01, 5.7000e+01, 6.0000e+01, 6.1000e+01, 6.3000e+01, 6.7000e+01, 6.8000e+01, 7.1000e+01, 7.6000e+01, 7.7000e+01, 8.0000e+01, 8.6000e+01, 8.7000e+01, 8.8000e+01, 9.1000e+01, 9.8000e+01, 9.9000e+01, 1.0000e+02, 1.0400e+02, 1.1400e+02, 1.1600e+02, 1.2100e+02, 1.3300e+02, 1.3400e+02, 1.3500e+02, 1.4200e+02, 1.5600e+02, 1.5700e+02, 1.5900e+02, 1.6700e+02, 1.8600e+02, 1.8700e+02, 1.8800e+02, 1.9000e+02, 2.0000e+02, 2.2600e+02, 2.3000e+02, 2.3100e+02, 2.4600e+02, 2.9200e+02, 2.9500e+02, 2.9900e+02, 3.0000e+02, 3.2000e+02, 4.4200e+02, 4.4500e+02, 4.5200e+02, 4.5700e+02, 4.8500e+02, 1.0645e+04, 1.1602e+04, 1.3856e+04, 1.6537e+04, 1.7642e+04, 2.2227e+04]

y = [0.57583333, 0.73833333, 0.81666667, 0.86016667, 0.88616667, 0.90266667, 0.91416667, 0.92333333, 0.93033333, 0.93633333, 0.94133333, 0.946, 0.94966667, 0.95333333, 0.95633333, 0.95866667, 0.96133333, 0.9635, 0.9655, 0.96683333, 0.96866667, 0.97016667, 0.97166667, 0.97266667, 0.97383333, 0.97483333, 0.9758, 0.97633333, 0.9775, 0.97783333, 0.979, 0.9795, 0.97983333, 0.98083333, 0.9818, 0.982, 0.982, 0.983, 0.983, 0.984, 0.984, 0.985, 0.985, 0.986, 0.986, 0.987, 0.987, 0.988, 0.988, 0.988, 0.989, 0.989, 0.989, 0.99, 0.99, 0.99, 0.991, 0.991, 0.991, 0.991, 0.992, 0.992, 0.992, 0.992, 0.993, 0.993, 0.993, 0.994, 0.994, 0.994, 0.994, 0.995, 0.995, 0.995, 0.995, 0.996, 0.996, 0.996, 0.996, 0.996, 0.997, 0.997, 0.997, 0.997, 0.998, 0.998, 0.998, 0.998, 0.998, 0.999, 0.999, 0.999, 0.999, 0.999, 1., 1., 1., 1., 1., 1. ]

plt.xscale("symlog")
plt.scatter(x, y)
plt.show()

Actual outcome

Using 3.1.0

Expected outcome

Using 3.0.3

Especially look at the Y axis, we lost the 0.5 value and 0.7 too. Worst, I think (not clear here in this picture) that the points are shifted from the actual X values

Matplotlib version

Operating system: Ubuntu 18.04 LTS

Matplotlib version: 3.1.0

Matplotlib backend : TkAgg

Python version: 3.6.7

Installed with pip3