Thank you for reply!
I created my custom board, so there are no diodes. Tx and Rx data lines are connected to the STM32 with BSS138 mosfets to shift 1.8 to 3.3 volts logic levels.
I had an idea that maybe the problem that is MCU suddenly triggers the power key pin and this causes the reboot. But it is okay, there is 0v on it while it`s working even in the moment of reboot