Are you using any widgets for a stream or just the SRT? I found my performance in a set of widgets I'd been using rather than the SRT tool itself.

the lag you're talking about might actually be the game lagging because its loading in new areas, it happens often if you're speedrunning, pausing the game lets it load so the frames become stable, still not sure if thats the case but yeah

Essentially anything that reads from the JSON feed. In the SRT tool there is an example SampleJSONDisplayPage.html page that looks at an exposed address and displays data.

I found when I was developing mine that the speed at which it checked the feed for data caused frame drops. However, if you're not using anything like this then feel free to ignore me :)