modbus communication is freezed

I have a siemens PLC as master and two Arduino UNOs as slaves. my modbus (RTU) communication has been freezed for randomly days (sometimes 15 days and sometimes 40 days).

what is the problem?

what is the problem?

Either the code you didn't post, the hardware you didn't adequately describe, or the power supply that you didn't even mention.

PaulS:
Either the code you didn’t post, the hardware you didn’t adequately describe, or the power supply that you didn’t even mention.

I’ve used 12 v DC power supply(ac to dc), that changed 220 vAC to it.

there is not any solution?

there is not any solution?

There were three possibilities listed in reply #1.

How many of them did you address?