I’ve noticed that when jsreport starts lagging, it’s usually either a massive data object being passed to the template or Chrome's memory management hitting a wall.
One thing that really helped me was switching to the headless Chrome launch strategy in the config, or making sure I wasn't doing heavy data processing inside the Helpers - doing that before passing it to the engine makes a huge difference. Also, if you're using a lot of images or heavy CSS, try checking the "Scripts" execution time in the profiler; sometimes a single synchronous loop in a helper can hang the whole render.