spyder: Stuck on "Connecting to kernel..." after matplotlib instalation with Spyder 5.1.5

Issue Report Checklist

• Searched the issues page for similar reports
• Read the relevant sections of the Spyder Troubleshooting Guide and followed its advice
• Reproduced the issue after updating with conda update spyder (or pip, if not using Anaconda)
• Could not reproduce inside jupyter qtconsole (if console-related)
• Tried basic troubleshooting (if a bug/error)
  • Restarted Spyder
  • Reset preferences with spyder --reset
  • Reinstalled the latest version of Anaconda
  • Tried the other applicable steps from the Troubleshooting Guide
• Completed the Problem Description, Steps to Reproduce and Version sections below

Problem Description

I recently updated to Spyder 5.1.5. and I checked that everything was working. Then I installed matplotlib and after this installation it was stuck on “Connecting to kernel…”

I also ran conda install jupyter_client=6.1.12 freetype=2.10.4 and restarted Spyder but there is no solution.

What steps reproduce the problem?

1. Installing matplotlib after upgrade to Spyder 5.1.5

What is the expected output? What do you see instead?

Paste Traceback/Error Below (if applicable)

PASTE TRACEBACK HERE

Versions

• Spyder version: 5.1.5 None
• Python version: 3.9.7 64-bit
• Qt version: 5.9.7
• PyQt5 version: 5.9.2
• Operating System: Linux 4.15.0-161-generic

Dependencies

# Mandatory:
atomicwrites >=1.2.0          :  1.4.0 (OK)
chardet >=2.0.0               :  4.0.0 (OK)
cloudpickle >=0.5.0           :  2.0.0 (OK)
cookiecutter >=1.6.0          :  1.7.2 (OK)
diff_match_patch >=20181111   :  20200713 (OK)
intervaltree >=3.0.2          :  3.1.0 (OK)
IPython >=7.6.0               :  7.29.0 (OK)
jedi >=0.17.2;<0.19.0         :  0.18.0 (OK)
jsonschema >=3.2.0            :  3.2.0 (OK)
keyring >=17.0.0              :  23.1.0 (OK)
nbconvert >=4.0               :  6.1.0 (OK)
numpydoc >=0.6.0              :  1.1.0 (OK)
parso >=0.7.0;<0.9.0          :  0.8.2 (OK)
pexpect >=4.4.0               :  4.8.0 (OK)
pickleshare >=0.4             :  0.7.5 (OK)
psutil >=5.3                  :  5.8.0 (OK)
pygments >=2.0                :  2.10.0 (OK)
pylint >=2.5.0;<2.10.0        :  2.9.6 (OK)
pyls_spyder >=0.4.0           :  0.4.0 (OK)
pylsp >=1.2.2;<1.3.0          :  1.2.4 (OK)
pylsp_black >=1.0.0           :  None (OK)
qdarkstyle =3.0.2             :  3.0.2 (OK)
qstylizer >=0.1.10            :  0.1.10 (OK)
qtawesome >=1.0.2             :  1.0.2 (OK)
qtconsole >=5.1.0             :  5.1.1 (OK)
qtpy >=1.5.0                  :  1.10.0 (OK)
rtree >=0.9.7                 :  0.9.7 (OK)
setuptools >=49.6.0           :  58.0.4 (OK)
sphinx >=0.6.6                :  4.2.0 (OK)
spyder_kernels >=2.1.1;<2.2.0 :  2.1.3 (OK)
textdistance >=4.2.0          :  4.2.1 (OK)
three_merge >=0.1.1           :  0.1.1 (OK)
watchdog >=0.10.3             :  2.1.3 (OK)
xdg >=0.26                    :  0.27 (OK)
zmq >=17                      :  22.2.1 (OK)

# Optional:
cython >=0.21                 :  0.29.24 (OK)
matplotlib >=2.0.0            :  3.4.3 (OK)
numpy >=1.7                   :  1.21.2 (OK)
pandas >=1.1.1                :  1.3.4 (OK)
scipy >=0.17.0                :  1.7.1 (OK)
sympy >=0.7.3                 :  None (OK)