I’ve had them “break in” during the first cuts.
In many, you can hear a sudden jump in rpm with the same load on the saw.
I’m assuming that it must be the rings seating, but I don’t really know.
Many of us believe that the M-Tronic saws have a built in “limp mode” for X amount of running time. I have no firm proof, but it seems they all start to run differently after a certain amount of run time. It’s different than the older ones that slowly get better. The newer ones seem to have an abrupt change in their running characteristics. YMMV
May explain your 500i experience.