circuit working when connect jtag ground or cro ground

[KN.2]

hi,

we are developing HMI using stm32f746 microcontroller it has 7 inch tft display,sd ram,norflash,usb,sdcard,ethernet and wifi.and we are devoloping a code for each sections one by one,till now tft display ethernet uart,wifi sections are completed,when test the wifi code if i press reset the microcontroller is noy getting on(cpu run led is not blinking,no display )if i connect the j tag ground alone with this its working similarly when i connect the negative probe of cro with any ground terminal its working but its not a fixed issue this is happening in random manner.any idea???