[Going underwater slows down your land melee]

Yeah I haven't had the chance  to do this in a public run. Kind of didn't want to distrupt a farm or something just to mess around with water but it does seem host isolated because I zoned in on a water enterance and I wasn't hosting and it was fine with my Zaw. I can't think of anything else to check atm.

[Going underwater slows down your land melee]

Yeah this happened to me as well. 

I was at Uranus - Ophelia and I went back and replicated it just for a small while. Even if you have another weapon when you go into the water, attack speed on the melee in land is still affected. The only way I lost the slow (which also messes with normal movement outside of melee attacks some of the times as well) is to die and force revive. If you get a revive from someone it stays. Shooting speed is unaffected from what I can tell. Quick melee and primary focus melee are affected one and the same. Shooting or meleeing in the water doesn't reset it, nor does anything to do with using archwing abilities. 

I went back for my last time with Galatine Prime. No attack speed slow. This looks like (at least with what I was using) is limited to zaws. Before activating the alarm in the water I couldn't make the attack speed slow happen with Galatine and after I activated it nothing happened. I went to a small water room and another submarine like room to see the water in there with the Galatine, no slow down occurred but it did with my Zaw. 
 

[Raptor Fight Bugged]

So just to add to this in attempts on seeing how bad it is and because I needed the frame parts from this boss. 

After killing the raptor enough time to get him to lvl 90, I only managed to get one Gravity Conveyor before I stopped trying. I noticed that if the bomb exploded during the raptor talking so Lotus interrupts him, then it exploded for me at least once. Other tests I did was letting it explode on me, throwing it in and trying to land dead center, killing the raptor before it came out, throwing the bomb in as soon as I could, and throwing it in at the last second. All of these failed. I was not able to recreate the explosion during him talking. So within the 3 attempts I made at the boss, I've been only able to kill one conveyor. 

Even more interesting is that I kept making the bombs explode enough that when I quit I still got the mark of death from the stalker on my second attempt when I got him to lvl 60-ish. My first attempt the moment I noticed them not exploding after my first three attempts I went back in and noticed that. So after 9 bomb attempts you can get a mark of death from the stalker.