Logic Remote iPad app no longer able to control Logic Pro X
I found that deleting the Logic Remote device in Logic Pro X's Control Surface Setup screen fixes the issue:


In Logic Pro X, go to Logic Pro X > Control Surfaces > Setup...
Find the device that is representing the iPad's Logic Remote app.
Right-click the entry and select Delete
Close down the iPad's Logic Remote app and restart it.
Wait for it to connect to Logic Pro X and the mixing controls will work fine again.