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[BUG] - some plots disappearing/not displaying properly after update_data()/update_gfx() calls

See original GitHub issue

Requirements (place an `x` in each of the `[ ]`)**

I realize finplot is not a web lib. (Hint: it’s native!)
I’ve read the snippets and not found what I’m looking for.
I’ve searched for any related issues and avoided creating a duplicate issue.
I’ve updated finplot (pip install -U finplot).
I’ve supplied the required data to run my code below.

Code to reproduce

import finplot as fplt
import pandas as pd
import io

# -- make a chart with 2 row with a plot in each --

data = """time,vol
          2020-08-01T00:00:00,134.18994254
          2020-08-01T00:05:00,28.68361201
          2020-08-01T00:10:00,95.9841699
          2020-08-01T00:15:00,25.52036882
          2020-08-01T00:20:00,32.99362203
          2020-08-01T00:25:00,272.87459159
          2020-08-01T00:30:00,65.2196942
          2020-08-01T00:35:00,74.78479433
          2020-08-01T00:40:00,46.8928428
          2020-08-01T00:45:00,42.36720822
          2020-08-01T00:50:00,22.21062411
          2020-08-01T00:55:00,39.78889563
          2020-08-01T01:00:00,33.73745861
          2020-08-01T01:05:00,36.34563807
          2020-08-01T01:10:00,36.1138157
          2020-08-01T01:15:00,40.76047654
          2020-08-01T01:20:00,22.53141467
          2020-08-01T01:25:00,18.07777984
          2020-08-01T01:30:00,29.34292546
          2020-08-01T01:35:00,34.43111442
          2020-08-01T01:40:00,15.24503765
          2020-08-01T01:45:00,26.6317692"""

df = pd.read_csv(io.StringIO(data))
df = df.astype({'time':'datetime64[ns, UTC]'})

ax1,ax2 = fplt.create_plot("improper plot problem", rows=2, maximize=False)

plot1 = fplt.plot(df["time vol".split()], ax=ax1, legend="test1")
plot2 = fplt.plot(df["time vol".split()], ax=ax2, legend="test2")

# ** df is updated with additional data here, but is omitted for clarity **

# -- now update the charts with updated df (à la issue #131 example) --
plot1.update_data(df["time vol".split()], gfx=False)
plot2.update_data(df["time vol".split()], gfx=False)

# --> these calls cause a blank chart on the ax2 plot
# (a zoom or scroll on the chart will cause the plot to reappear)
plot1.update_gfx()
plot2.update_gfx() 

fplt.show()

Describe the bug

On a 2 row chart, updating the plot data will cause the second plot to not dispay properly.

This appears to be a bug introduced in commit 1190e8a (on 2021-07-08) where round() is replaced with _round(). Roll back to the previous commit and the bug disappears.

Expected behavior

Both plots should remain visible after update_gfx() call. Currently, a manual scroll or zoom is needed to cause the second plot to appear after the update_data()/update_gfx() calls.