i still think it is caused by the ground . maybe you can check with a multimeter to see if it grounded well
the U9 Pin9 is for signal out input to U9, and then out from the U9_Pin8. you can check if the voltage on these 2 pins .if the Pin8 is normal, maybe the problem caused by the signal_generator connector or the wires between the connnector and U9_pin8,
if the U9_pin9 is normal but the U9_pin8 is abnormal, you need to check if the power of U9(Pin4 for 3.6V,pin7 for gnd) is normal, to see if the U9 is in normal state.
if the U9_Pin9 is abnormal , you may need to check the Pin_59 of the MCU is normal, maybe leaded by abnormal solder.