Can't run Spyder3 after attempting to install Spyder4

[Alexander Christner]

I recently tried upgrading from spyder3 to spyder4 on my Ubuntu via the instructions at https://github.com/spyder-ide/spyder/releases

However, something went wrong and I can no longer run spyder3.

Everytime I do, I get a warning saying:

"

Spyder crashed during last session.

If Spyder does not start at all and before submitting a bug report, please try to reset settings to defaults by running Spyder with the command line option '--reset':
spyder --reset

Warning: this command will remove all your Spyder configuration files located in '/home/christner-alex/.config/spyder-py3').

If restoring the default settings does not help, please take the time to search for known bugs or discussions matching your situation before eventually creating a new issue here. Your feedback will always be greatly appreciated.

"

and my crash log fills with:

"

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/spyder/app/mainwindow.py", line 3126, in main
mainwindow = run_spyder(app, options, args)
File "/usr/lib/python3/dist-packages/spyder/app/mainwindow.py", line 3023, in run_spyder
main.setup()
File "/usr/lib/python3/dist-packages/spyder/app/mainwindow.py", line 932, in setup
from spyder.plugins.ipythonconsole import IPythonConsole
File "/usr/lib/python3/dist-packages/spyder/plugins/ipythonconsole.py", line 25, in <module>
from jupyter_client.connect import find_connection_file
File "/home/christner-alex/.local/lib/python3.6/site-packages/jupyter_client/__init__.py", line 4, in <module>
from .connect import *
File "/home/christner-alex/.local/lib/python3.6/site-packages/jupyter_client/connect.py", line 35, in <module>
from jupyter_core.paths import jupyter_data_dir, jupyter_runtime_dir, secure_write
ImportError: cannot import name 'secure_write'

"

I tried resetting, but the same error occurs.

I tried uninstalling and reinstalling spyder3 with

"sudo apt-get install spyder3", but even after that the error doesn't change.

What else can I do?