Welcome to the Netskope community. The likely reason for this is that many development tools such as Powershell don't trust the system certificate store for TLS inspection. When you bypass Netskope by disabling the client or the certificate pinned application, you are no longer inspecting this traffic so it works. There's usually two options for apps that don't trust the system certificate store:
1. Bypass the application from inspection via a steering or TLS inspection bypass (easiest resolution but limits visibility)
2. Import the Netskope certificate into the application so it trusts the certificate or configure the application to trust the system certificate store.
You've already performed the first step but if you'd like to have Powershell trust the system store, you can follow the instructions here:
Netskope Sales Engineer - North Florida