I have upgraded several on-prem platform servers following the checklist for 11.9.1. Every single server has run into the same problem when it comes to installing the Sample Data application (and I cannot install the templates that depend on them). I have tried installing Sample Data from the forge, downloading the OAP and installing through the development studio, and loading the OAP directly on the server and uploading/publishing via ServiceCenter. They all give me the same error message below:

Error during external Solution publish: Index was outside the bounds of the array.

All of the servers were upgraded from 11.7.2 to 11.9.1. Two of the servers had not had any applications installed on them outside of the initial OutSystems install.