Relay on cem+ rack

I have 4 ESR36 Racks with CEM+ Modules running software version 3.1.2.9.0.38

I have a number of ER15 modules 

Some are older eg P/N 7070A2105 S/N245292

Some are newer eg  P/N 7070A3305.  S/N 318184

All of the relay modules work in rack 1, 3 and 4

However only the newer modules work in rack 2 

I'm at a loss as to why this is 

I have spoken to a few folks at etc nobody seems to be able to solve this 

All racks installed at the same time (2011 I believe)

All racks are on the same group and same network 

Can anyone help with this?  

Thanks 

Phil

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