SIM800C - CME ERROR: 15 SIM wrong & CME ERROR: 10 SIM not inserted

I am making a GSM Tracker with SIM800C module. After deploying it into vehicles.. It works fine.. but after some days, it starts responding as CME ERROR: 15 SIM wrong for command AT+CPIN? & CME ERROR: 10 SIM not inserted for commands required to build TCP Connections. The Commands are written below.

  delay(100);
myGsm.println("AT+CIPSHUT");
delay(1000);
printSerialData();

myGsm.println("AT+CIPMUX=0");
delay(2000);
printSerialData();


also I checked the potential between SIM800C's SIMVCC & GND it was 1.8 V which is fine. I am not able to understand the cause of the errors.I have attached the Schematic Of device.[![enter image description here][1]][1] somebody, please suggest the solution as it gets disconnected with the server in between the journey & tracker losts.

Edit:- Here are my Some Observations :-

1. On Soft resetting the Module i.e. by giving AT Command AT+CFUN=1,1, error resolves but I don't want to use this as this is a temporary solution. it starts giving the error again.
2. There is no effect of hard resetting the MCU.
3. The error resolves after reinserting the battery but this will not work as I can't do this from server side.

Please, somebody, tell the cause of the problem so that I can take it as use-case in my development.

• Vibration? Unstable power supply? Try soft-resetting the module when it replies with a SIM error. – filo Aug 8 '18 at 10:09
• On Soft resetting the Module i.e. by giving AT Command AT+CFUN=1,1, error resolves but I don't want to use this as this is a temporary solution. it starts giving the error again after some time. please tell the cause of the error. and how to check the vibration..? @filo – bandejiya Aug 8 '18 at 10:57
• Run it for one week on the table. If no failures happen then simply it is the environment in the vehicle that affects your device. I would bet on supply voltage (add capacitors or a better power supply) and mechanical assembly/vibration. – filo Aug 8 '18 at 10:59
• Exactly.! it works fine on the table. & I have added 100nf capacitor with VBATT pin of SIM800C, is there any problem in this..? & please throw some light on mechanical assembly/vibration. – bandejiya Aug 8 '18 at 11:07
• How? You did not post the PCB, nor photos. – filo Aug 8 '18 at 11:15