Master Display Question

[Natch]

Hopefully, this will be my last request for info.
With an A128 at the bow, matched with the CPT-100 transducer on the trolling motor, I have a water temp reading, from the temp sensor mounted in the transducer.
With the A127 mounted at the console, I run an in hull transducer for 2D sonar and the CP-200 for Side Vision. The Side Vision transducer does not provide water temp. The units are linked with a network cable, but are not connected with a sea talk cable.
With the bow unit on only, I have a water temp reading in my data box. If I turn both units on, regardless of which unit is selected as the Master Display, the water temp remains at 32 deg.
Any ideas on a resolution to this, would be appreciated.

Thanks