I used kurama kisame samehada roshi lineup in arena and swb for over 8 months.

His buff to combo cannot be removed.

If happens you fail in triggering the cd reduction is simply due to bad luck or higher combo stats from the enemy.

The reason why is not removed is in the description, if you read it:

As you can see, it doesn't say: 'and naruto' s combo rate will increase by 80% for 1 round' but says 'until the end of the round', that means if we are in round 2 is up until the end of round 2, doesn't matter by how many rounds you reduce its duration (that's what buff removal effects do), since is not linked to an amount of rounds but to the very specific round you are in in that moment.

A different matter is the immunity to debuffs he grants to shinobi alliance ninjas.

That one gets removed, or better say its duration gets reduced to 0 rounds.