NB-Extensions not loading correctly after notebook refresh / copy

Occasionally after refreshing or copying (i.e. using "make a copy" from the file menu) my notebook, the nbextensions fail to load correctly. In general these notebooks are pretty large, 10-100s of MB. I wonder if this is related to saving issues. Not having the extensions becomes very bothersome as, with large notebooks, I really rely on the TOC and collapsible headers for navigation.

If I create and open a new notebook, the extensions load just fine.

I eventually end up fixing this by some combination of turning the extensions off and on again, refreshing the notebook, restarting jupyter, and if all else fails making a new notebook and copying the large notebook contents into it.

I'm using jupyter version 4.3.0, notebook version 5.2.1.

I'm using these extensions at the moment:

Start by reproducing the failure with a large notebook after refresh and “make a copy,” using Jupyter 4.3.0 and Notebook 5.2.1 with the extensions shown in the issue. Compare extension loading with a newly created notebook and check whether toggling extensions, refreshing, or restarting changes the result. Done means the extensions reliably load after refresh and copy operations.

Written by the indexing model from the issue text.