If you hand hold the drone and move it around, does the gimbal hold the horizon??? If not, I would check your gain curves. I don't own a
P4P V2, but this just looks like a gimbal gain curve issue to me. Don't ask me where this option exists in software. I would start with the Camera icon in the app.
Also, with the drone off, I would check to see if there's any restriction in the gimbal's roll axis. I might guess that there's a piece of grass or something stuck in the roll motor slowing down the gimbal.
D