It is possible to hide stock transfer requisitions releases from MRP using BAdI MD_CHANGE_MRP_DATA. Please take a look on the following document and check if this BAdI is implemented on your system:
Making an element not relevant to MRP or MD04 using BAdI MD_CHANGE_MRP_DATA
If the BAdI is not implemented, you must check in debug why the MRP element is not displayed on MD04 and you can follow the steps described on the following document:
How to analyze transaction MD04 in debug
BR
Caetano