Smartcard communication gets disturbed by communication on another UART, what can be the reason?

[SPaes.1]

UART2 is used for as smart card communication. (sign data)

UART1 is used for communication from outside

It looks like the communication to the smart card can get disturbed by communication on UART1

result invalid signature.

The interrupt priority of UART2 (smartcard) and UART1 are the same

I'm using STM32F072C8Tx, interrupt based communication with the secure module (HAL_SMARTCARD_Transmit_IT)

[CYANG.1]

Hi SPase,

Which platform did you use? You could check if the UART lines are in parallel and could impact to each other on PCB.