So for me electron apps are simply only viable if i absolutely need them, and i curse the name of anyone who thinks they're a good idea for anything but rapid prototyping every single day.
Mind, i'm aware you have what you have right now, and going another path would be quite the expenditure. However i think it's not much to ask to refrain from calling it native, when it's actually electron, and thus helping people impacted by this kind of performance issue figure out that your app is one of the contributing ones.
That said, i don't use Postman, heard of it the first time today. But you might be able to reproduce some of the issues by loading a very animation-heavy imgur page like https://imgur.com/a/0L8Bu , scrolling to the gifs, maybe zooming out a little to get more on screen, and starting up a bunch of different electron apps. Particularly helpful would be using https://technet.microsoft.com/en-us/sysinternals/processexpl... to keep an eye on the interrupt CPU usage. Once you start seeing lots of red activity you're getting close.