Hanging the Arduino(STM32) when receiving a pulse from Sim800L

Hi everyone,

I have the following hardware context:

Arduino STM32
Bulk converter DC-DC
Wiring method: The serial ports are connected without any resistors.

About a couple of weeks ago, I started a remote control project. On the breadboard, everything was perfect and the codes worked perfectly. However, after transferring my circuit to the PCB board everything changed. NOW I can't receive SMS while AT commands show OK. Even, I removed all codes in LOOP and simply wrote a reading serial pin (RX) but when an SMS coming to Arduino, it doesn't work anymore. When the message pulse reaches the Arduino from the sim800 module, the Arduino hangs and does not continue the loop. Also, I tested all serial ports in my controller module and the results were the same.
Do you think hardware components are damaged?
Has anyone experienced this problem?