I keep getting message about fixed wing mode on my P4 but so far not able to get it to go into the mode. I have a Mavic and am very familiar with the mode so am doing all that's required. Any ideas?

Maybe it relates to you having a Dji mavic. I have a Dji phantom 4 and it never happens to me.

This wouldn't be related to the fixed FPV gimbal mode on the Phantom, would it?  

There isn't a fixed wing mode available for the P4. The message is most likely due to your Mavic.