Thanks Tomas. I wonder if playing with ACTLR[20:16] aka DISDI has any impact on this test? I don't think that dual issue can be completely disabled in case it's a factor here? Maybe set it to 0x3F and see if that makes any difference?
https://developer.arm.com/documentation/dui0646/a/Cortex-M7-Peripherals/System-control-block/Auxiliary-Control-Register?lang=en
