Hey Jasper, welcome here! Feel free to Introduce yourself 
It’s difficult for us to know exactly why that happens, it’s an issue we’ve not been able to replicate on our end. It might be because of a specific system configuration or restrictions imposed by IT.
In regards to installation methods for v2 Connectors, Manager is just a handy tool that lets you update/install/remove Connectors and manage accounts in a single place. Behind the scenes, Manager also downloads the exe installer and runs it upon installation.
You might have seen that we have released v3 Connectors recently and have deprecated Manager. So from now on, you can get them directly from: Log in | Speckle