Dear Raul,
I believe you have to run MRP individually for Plant A & Plant B in order for the ROH's requirement in plant B to be triggered and planned.
1st option :
You may config the Scope of planning and config the plants in sequence. Use MD01 to execute the MRP run via scope of planning. In this case, MRP will trigger for both plants.
2nd option :
If you are executing by plant, execute MRP via MD01 for plant A and then proceed to run for plant B.
Please try and feedback.
Thanks
Karthik