Ok we found the solution.
We modified the test scripts you asked to run to this simple code:
We executed the ruby scripts and it provided this error:
https://serverfault.com/questions/856333/foreman-smart-proxy-microsoft-dhcp-unknown-error-5
Turns out I either didn’t start the smart-proxy previously as local Administrator like I used to with the old version.
I did add my own user to the DHCP administrators group now and it’s working both with and without elevated Administrator rights.
So for anyone having the same issue, please check under what user the smart-proxy runs and if this user is either a local admin on the DHCP controller or a user in the DHCP administrators group.