widgets failing to load after notebook closed and reopened

[danquix0te]

I've been working through declarativewidgets demos. It works ok for me as I'm building the workbook. But when I close and reopen the notebook I have errors that show up on both terminal and browser console. I create a new notebook, do the same thing - works fine there. Close/re-open and doesn't work. I must have something wrong with env? Not sure

terminal:
C:\Users\dbrown>C:\ProgramData\Anaconda3\Scripts\jupyter notebook
C:\ProgramData\Anaconda3\lib\site-packages\urth\widgets_init_.py:7: UserWarning: The urth package name is deprecated. Will be removed in version 0.7.0. Use 'declarativewidg
ets' instead.
warn("The urth package name is deprecated. Will be removed in version 0.7.0. "
[I 17:07:35.092 NotebookApp] Loading urth_import server extension.
[I 17:07:35.263 NotebookApp] Serving notebooks from local directory: C:\Users\dbrown
[I 17:07:35.263 NotebookApp] 0 active kernels
[I 17:07:35.264 NotebookApp] The Jupyter Notebook is running at: http://localhost:8888/?token=2627a9fd7bf57c7ccb00efe2e1500511e2c4c6ea1441afa3
[I 17:07:35.265 NotebookApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 17:07:35.266 NotebookApp]

Copy/paste this URL into your browser when you connect for the first time,
to login with a token:
    http://localhost:8888/?token=2627a9fd7bf57c7ccb00efe2e1500511e2c4c6ea1441afa3

[I 17:07:35.484 NotebookApp] Accepting one-time-token-authenticated connection from ::1
[W 17:07:53.368 NotebookApp] 404 GET /notebooks/urth_components/paper-input/paper-input.html (::1): No such file or directory: urth_components/paper-input/paper-input.html
[W 17:07:53.376 NotebookApp] 404 GET /notebooks/urth_components/paper-input/paper-input.html (::1) 9.01ms referer=http://localhost:8888/notebooks/Untitled2.ipynb
[I 17:07:53.655 NotebookApp] Kernel started: 158441e7-1e49-4f1d-895e-48173d611911

browser console:

[danquix0te]

I've been trying to build a consistently working DW environment for about a week with no consistent success. I've deployed the docker environment at jupyter-incubator/dashboards_setup which seems to have suffered from bitrot (Polymer changes?) In any case, unless someone can point me to a canonical way to arrive at a stable working environment, I'm afraid I'll have to abandon my efforts to use this work.