The Warwick leap part is intentional by design, he can't be disabled during that form of his Q. You should find that the damage from your ult is still inflicted.
As for the other one, that seems bugged.. Warwick is immune to disables during his ultimate leap, so if you use your ultimate early it should not push him at all. If you buffer it perfectly, it should in theory activate the knockback after he lands, at which point Warwick can be affected by disables such as your ult's knockback, but that should break him out of the channel.
The three possible conditions should be, if I understand the mechanics properly
- You use your ultimate early and the knockback frame occurs during his leap, which has no effect
- You buffer your ultimate at the right time and the knockback frame occurs when he is channeling the suppression, breaking him out of it
- You attempt to use your ultimate too late and get suppressed, but he stays in melee range and the ult is never used, should still be available to cast.
Number 2 may not be possible depending on what frame after the ability cast Xin's ultimate knocks enemies back. But in any case, if the ultimate occurs and creates the circle around Xin, Warwick should either have his channel interrupted or be channeling on you from melee range.