Why does my Siemens S7-1200 PLC keep losing communication with the on-site frequency converter?

I am responsible for the maintenance of a plastic injection molding production line. The Siemens S7-1200 PLC communicates with the Siemens G120 frequency converter via Profibus DP to control the speed of the conveyor belt motor. Recently, the communication between the PLC and the frequency converter has been frequently disconnected (about 2-3 times per shift), and the PLC diagnostic buffer shows "DP slave communication failure".

After disconnection, restarting the frequency converter can temporarily restore communication, but the problem recurs after a few hours. We have checked the cable connections at both ends and replaced the DP connector, but the issue still exists. What are the possible causes of this intermittent communication loss, and how can I troubleshoot and solve it?