Here are my steps for installing Jupyter Lab and the Git extension, and then trying to troubleshoot the extension version mismatch problem:
Specs: MacOS Mojave 10.14.6, Jupyter Lab 3.0.5
1. I installed Jupyter Lab using pip3 install jupyterlab
2. I installed the Jupyter Lab Git extension directly from Jupyter Lab's Widgets Manager:
3. After doing so I received additional instructions:
4. I clicked 'OK' and then ran pip3 install jupyterlab-git
5. Back in Jupyter Lab, it said a build was needed to include the latest changes, so I selected 'Rebuild'
6. The build was successful, and I clicked on 'Save and Reload'
7. Upon reloading, I received the following message:
8. I followed the instructions and ran pip3 install --upgrade jupyterlab-git
9. I went back to Jupyter Lab and clicked "Dismiss" on the message.
10. I closed and reopened Jupyter Lab via terminal. After reopening, the same "failed to load" message appeared.
11. I then found this link troubleshooting a similar issue.
12. I followed the advice by running all of the below commands (with pip3, and fixing spelling errors):
13. The user then suggests the following to make sure everything worked OK. So I closed Jupyter Lab again, and ran all of the following:
14. Running jupyter serverextension list I get the following, which I think looks OK:
15. Then I ran pip3 list and get back: jupyterlab-git 0.23.3 (so Git extension version 0.23.3, which according to the GitHub extension page at the time of me writing this is the most current (non-beta) version).
16. Then I ran jupyter labextension list and see nothing related to the Git extension, which is not expected per the above user's screenshots (it's supposed to show the Git Extension here):
17. Now here's one last thing: When I go back and install the Git extension via Jupyter Lab's Extension Manager (like I had done initially), and then I run jupyter labextension list again, I see that the Git extension is the "pre-release" version v0.30.0b1, which would likely be why way back in step 7 I got the error message that the frontend and backend extensions did not match.
And here's where I'm stuck. I can't seem to get these two extension installations to match (or to ever have the extension icon show up in the side panel).
And around and around I go...
EDIT: Possible solution.
After reading my own question here, I thought maybe I should try to install the "pre-release" Git extension version to match the other version, and that seems to have worked. I just didn't think it was best practice to use "pre-release" or beta versions, so that had not occurred to me until just now. So I'm not going to "solve" my own question here, because I'm just not sure this is the best solution... But is it?
I ran this: pip3 install jupyterlab-git==0.30.0b1 and now I'm no longer seeing any version mismatch errors, and the Git extension icon is finally showing up in the side panel.
question from:
https://stackoverflow.com/questions/65851738/issues-installing-jupyter-lab-git-extension-mismatched-front-backend-versions 
