I am talking about the feature that a Paladin with Oath of the Open Sea gets at lvl 3:

As an action, you channel the sea to create a thick cloud of fog that surrounds you for 20 feet in all directions. The fog moves with you, remaining centered on you and making its area heavily obscured. You and each creature within 5 feet of you instead treat the area as lightly obscured. This fog lasts for 10 minutes, spreads around corners, and cannot be dispersed unless you choose to end this effect (no action required).

Is there a way, fighting against this, to remove it or negate its effects? From what I read it is not a spell, so it can't be countered, it doesn't require concentration, lasts way longer than any fight, and moves with the paladin so you can't even move them away of this effect. Also it's not darkness, nor does it count as "invisibility", so all the divination effects designed to see through those will fail...

Is there something I missed?

The Oath of the Open Sea paladin (a third-party subclass from Critical Role) gets the Channel Divinity option "Marine Layer" at level 3:

As an action, you channel the sea to create a thick cloud of fog that surrounds you for 20 feet in all directions. The fog moves with you, remaining centered on you and making its area heavily obscured. You and each creature within 5 feet of you instead treat the area as lightly obscured. This fog lasts for 10 minutes, spreads around corners, and cannot be dispersed unless you choose to end this effect (no action required).

Is there a way, fighting against this, to remove it or negate its effects? 

From what I read, it is not a spell, so it can't be counterspelled, it doesn't require concentration, lasts way longer than any fight, and moves with the paladin so you can't even move them away from this effect. Also it's not darkness, nor does it count as "invisibility", so all the divination effects designed to see through those will fail...

Is there something I missed?