Whilst I have not had time to play with BP vs Postman, this behaviour usually observed when you are attached to a single parent process whilst 'child' processes are available.
Since you can run it via browser extension and via standalone application, it would be good to know, which option did you use
Like a browser that can have many child tabs, when you attach to a browser you might not necessarily attached to the part that you need to work on (it actually one of the downside and also an advantage of Blue Prism, as this ensures that you are 100% working on the correct part of the application and also it seems to be quicker instead of connecting to the whole application at the same time (larger application slower execution).
To fix this, 1st things 1st, try to deattach and reattaching with different ordinance but don't rely on it, this is simply to confirm that it is possible by default.
Then play with options to ensure you are attached first time.
Some application do need additional setup, but all except one of these in my experience would work with proper reattaching
