Here is some inconsistency in measurements taken:
There are 525 Kg of igneous rock sitting on the weight plate but the current pressure is only 225 Kg.
It happens when magma solidifies right on the weight plates.
P.S. After reloading the game the measurements are correct.
1. Load the game 2. Look that the weight plate current pressure equals to igneous rock located on it. 3. Wait for some magma appear and doors let it drop on weight plates (in a few seconds when regolith melts). 4. Look at the measurements again. New solidified magma added nothing to current pressure.