Opening notebook hangs Carnets but runs fine in Carnets+

I have a notebook which will not open in Carnets (I get a blank screen and Carnets appears hung). However, the same notebook opens fine in Carnets+. Running test versions of both apps.

No file or test is named. Start by reproducing the blank screen and hang with the reported notebook in the test versions of Carnets and Carnets+, then compare their notebook-opening paths; done means the notebook opens in Carnets without hanging and the case has regression coverage.

Written by the indexing model from the issue text.