Why does my phone stop working when I install the midframe

Hi everybody,

I have a weird problem with my galaxy S4 :

-A few weeks ago, the 4G started to be really very slow (way slower than 2G)

-Later, the SIM card was sometimes not detected and I needed to reboot the phone to make sure it was properly detected (and sometimes remove and insert again the SIM board)

-A few days ago, it started turning off by itself, and then never turned back on again.

The only way I found to fix it was to remove the midframe. That allowed me to turn the phone back on and get a good SIM board detection. I made a reset of the phone and that allowed me to recover 4G speed (I did not check the speed before the reset). If I install the midframe again, shortly after, the SIM board is not detected, the phone turns off by iteslf and it's impossible to turn it back on.

Does anyone as an idea of the diagnosis / root cause of this issue ? There is almost nothing on the midframe. Do you think it could come from overheating or bad electronic contact ? There are some contacts between the motherboard and the midframe but I don't understand their purpose.

Thanks,

Renaud