This is likely why the smoke profile of the Webers is far superior to anything else I’ve used. Traeger, camp chef, pit boss, Memphis etc. The industry has figured out that constant temp will not produce desirable results on pellet cookers. This is a huge departure from their thinking just a few years ago. Most are now intentionally programming fluctuations into the control module. Looks like you changed set point that caused the momentary spike? Looks like you did so just as the temps started to settle in? Huh. What does the time line represent as far as duration?
You can use both types of pellets, but they shouldn’t be exactly the same. They are different diameters. They should definitely combust differently. Game changer? Probably not.
Have you cooked on the grill or just testing it? If so, how are the results? I’ve never done any of those types of tests on my cookers. I have placed probes in cookers for brisket cooks before to allow me to adjust if I wanted. I personally don’t care what is going on minute by minute as long as I can produce top quality food. Obviously if you aren’t able to get results then I suppose it’s an issue.