Listener IP address offline
There can only be one IP address online for the listener at a given time.  Both IP addresses are registered in DNS (by default) even though one is offline, and when a client looks up the address of the listener, it will get two addresses.  If the client is "multi-subnet failover aware," it will try both addresses and use the one that responds

If the client is not "multi-subnet failover aware," it may try to use the IP address that is offline, and accordingly will fail to connect.  So if you start having intermittent client connection failures, this is why.

To have it only register the IP address that is online, change the RegisterAllProvidersIp setting on the listeners network name resource to 0.  See Multi-subnet Clustered SQL + RegisterAllProvidersIP + SharePoint 2013