When applying a surface load on one of the member's plates, it may happen that part of the load already lies outside of the plate's surface. In such a case, the full magnitude of the load would not be applied – part of the load would not be transferred and used in the calculation. This might be unsafe and unintuitive, that's why there is a warning message.
When a line or point load distribution area is larger than the plate assigned, a warning is displayed in the top left corner of the screen, and you should adjust the position or the area of action of the load.
This warning helps you overcome these situations and, therefore, improves the safety of the model.
Released in the IDEA StatiCa 23.1.1 patch.