Transform client works with primary ip but not with control port ip

On a fourier transform engine a customer claims that when he is connected on control ethernet port and use the control port ip on the client he cannot connect to the engine but when he is connected to the primary port and using the primary port ip he is able to connect with the engine. Is this a bug?

To me that sounds more like a network problem (Ip-Adresses, Subnets?)

I never had any problem with connecting to the engine.

Maybe he has the network adapter on the PC and the Primary Port on link local (IP Adress starting with 169…), therefore it works, but the control ip doenst work because it’s in a different IP range?