Issue was resolved thanks to the kind support of Dan from Leap Support. Just posting in case someone else faces a similar issue.
Building a scene containing Tracking + Haptics and the build kept closing. I narrowed it down to SensationCore being active resulting in the issue (possibly looking for python files but not finding them?). Going in the build file and moving the python36.zip from the Plugins folder into the X86_64 folder fixed it.
Ultrahaptics Core Unity Plugin: UCA-Beta-9-customer
Ultraleap Unity Plugin: 5.1.0