Siemens SPPAT3000 flickers the communication between 3 io modules of a rack

Good day sir,

My sppat3000 dcs has 2 cpu and 8 racks with et200m

No 7 rack has 8 io modules,
The last di,ai and ai these 3 card shows module not installed in module status in server pc.

We have done many things, but finally we have exchanged all of the io cards,backplane,im module and profibus connector with another working rack with same version and part numbers.

These io cards are working in that other rack are working fine. But still in thia rack the new working io cards ( the last 3 io cards) are showing same fault.

We have opened all the front connector of the rack. Still those 3 card's module status is flickering. Some times it works for 1 day, some times for 1 hour, sometimes for 10 minutes. But module status blinks after random interval.

It is to tell you that only these 3 cards are having this problem in this rack, the other 5 cards show no problem, they are always in module ok status.

Previously no one done anything with the program, machine was running, suddenly this problem came and cannot be solved yet.

Now you can say no 7 rack is fully replaced by no 6 rack including all hardware components et200m and backplane with same part number and version, but still the 3 card of that no.7 rack is flickering/ sometimes exists long time.( in diagonistic buffer in simatic manager it shows: module configured but not available).

But the original no.7 io modules are working fine in no.6 rack.

Please help sir.