Cache not getting used while rebuilding

[kp992]

Hi,

A project of quantecon uses jupyter book to build its html and pdf pages using myst. In the last couple of weeks we observed that the build is taking longer time on the CI because it is unable to use the cache. For example consider the following two CI workflow runs:

1. https://github.com/QuantEcon/lecture-python-intro/actions/runs/11118983947/job/30893458986?pr=551 - approx 2 weeks back
2. https://github.com/QuantEcon/lecture-python-intro/actions/runs/10396786335/job/28791423058 - Aug 15.

There is some minor difference that I observed in the logs of the step Build PDF from Latex. Previously sphinx was able to load the pickled environment as seen from the logs. But that log is no longer visible in the latest build.

Please help me to debug or fix this issue.

Thank you.