Changes to javascript are not getting reflected

[Poltto]

I'm running Ubuntu 20.04.

I'm trying to develop an extension for Ipyleaflet, and have followed the development advice like so:

git clone https://github.com/jupyter-widgets/ipyleaflet.git
cd ipyleaflet
pip install -e .
jupyter labextension develop --overwrite ipyleaflet

I'm running all of this within a conda environment created from environment.yml

Ipyleaflet then works fine on Jupyter Lab, great. I have then tried to first and foremost modify an existing javascript file (in this case the MagnifyingGlass.js -file), while using

jlpm run watch

And

jupyter lab --watch

The changes aren't reflected when reloading the jupyter lab -page in the browser. I have similarly tried creating an entirely new Javascript-file with the required view and model (MyClassModel and MyClassView), exported that file within jupyter-leaflet.js, and created the necessary new Python class (MyClass) in /ipyleaflet/leaflet.py. Importing the python class in a Jupyter Lab window works fine, but when trying to create an instance of the class the browser throws the error

Uncaught (in promise) Error: Class MyClassModel not found in module jupyter-leaflet.

I've tried doing everything three times over, rebuilding manually, and so on, but nothing seems to work. It seems that whatever javascript-changes are made, the python side never becomes aware of it. I have similarly tried this in a normal notebook environment (fulfilling the guidance in the official documentation for developing in jupyter notebook), but get the exact same result there.

Thank you for any help you may offer!