Once identical Deye SUN-12K inverters were connected in parallel and the alarm F29 Parralel_CANBus_Fault was displayed.
The reason turned out to be different firmware versions on the inverters:
Inverter ID: XXX HMI: Ver 1001-C03E MAIN: Ver 2006-1140-1807
Inverter ID: XXX HMI: Ver 1001-C031 MAIN: Ver 2005-1124-1807
After updating the firmware the problem disappeared.
To update the firmware, you need to connect the inverters to WiFi and contact Deye support, for example by email service @ deye.com.cn, describing the problem and serial numbers, they will update it remotely via the Internet, or contact the person who sold the inverters for help.
See also my article:
Connecting Tewaycell LiFePO4 batteries to inverters