This appears to be a compatibility issue with Sphinx Version: 3.2.0 (Released: Aug 8, 2020) and sphinxcontrib-matlabdomain Version 0.11.2 (Released: May 18, 2020).
When I run Sphinx Version: 3.2.0 and remove MATLAB API documentation this issue goes away
When I revert to Sphinx Version: 3.1.1 and add MATLAB API documentation this issue goes away
Documentation doesn't compile with Sphinx Version: 3.2.0.
Use the following package versions to compile documentation: