STM32L073RZT6 Hardware issue

[ABane.2]

Hello everyone,

I am working on STM32L073RZT6 microcontroller and I have designed my custom board using this mcu. I am facing issue related to reset. The microcontroller is getting rest automatically however the period is not fixed.

I understand the possible reasons for reset as per following image

 

Till now I have designed 3 boards using this microcontroller and in all the cases I am facing same issue. When I programmed the microcontroller for the first time it worked for 2-3 hours continuously in one board it worked for 6 hours too and after that it started resetting.

The voltage on reset pin is varying however the supply voltage is clean, you can refer the following image. 

The code that I have programmed in the MCU is simple LED blink code and also it sends data on USART5 the code is directly exported from the cube IDE and I have done very less changes I have also attached my main.c file for your reference..

I have tested following things

1. There is no drop on 3.3v line and supply is clean with ripples less than 70mv (Vpp)
2. There is no dry solder, I did touchup many times in all the three boards and it didn't helped.
3. Connections from debugger to MCU are correct and debugger is not resetting the MCU
4. Decoupling capacitors are connected near all the VCC pin and value is 0.1uF, I also changed the cap values to 4.7uF and it obviously didn't help.
5. Voltage on boot pin is 0v all the time.
6. 3.3v LDO is capable of providing 500mA of continuous current.
7. There is no bridge or short-circuit on any pin.
8. I also removed the external pull up on reset pin.
9. Removed the ferrite bead and shorted the line.

I am unable to figure out what's the issue, prior to this I have designed many boards based on M0, M4 microcontroller but I never faced such issue.

I have attached images of my schematic and layout for your reference, in attached layout you will observer AVCC pin is not connected anywhere I put a jumper there as it is a single sided PCB. please let me know how can I resolve this issue.

Thank you