Hello,
I had the same on the TFDi MD-11. And I believe that if the aircraft is coded a certain way using MSFS's icing model and loading, you will notice the ice weight on your payload manager. On the MD-11 you will see the extra weight on the FMC's payload page as a higher gross weight than the sum of your airplane weight and fuel weight.
This one I am not sure about. All I can think of is that maybe your intakes were clogged with and ice/or your inertial separators were closed. Leading to engines being chocked for air.