When inspecting the mesh closer there were some issues with its modelling, including overlapping vertices and polygons. Because of this, some changes were made to reconnect the overlapping vertices and remove the extra polygons. The lower half of the model was remade slightly differently to the original model, taking care to ensure that the model did not have any issues.
Below is the original model when the various issues were discovered. As my intention was to divide the model into smaller components, it was during this time that I found the issues with the model that were not visually apparent.
Below is the updated version of the model with the various changes made, as well as testing how to properly divide components for the model and use the Open Sub-Division modifier.