Danfoss VFD FC102 Modbus RTU Reset


I am using Unitronics PLC to read & write Danfoss VFD FC102 speed through Modbus RTU. In about 1~2 months, the communication down, reset VFD power supply then communication back to normal. It is repeat about 1~2 months.

Reset VFD power supply is not convenient for application.Anyone got other method to reset Modbus communication without reset VFD power supply? and what is the root cause of the communication down repeat?