I haven't had any of these problems with Poseidon, but I always make sure my hands are completely dry before opening it, and I don't allow the scoop to touch anything when I'm putting the powder into a bottle of water, I hold it a cm or so above the top of the bottle when tipping it in to avoid any moisture getting on it. My first tub of Poseidon lasted me about 6 weeks and I didn't see any signs of it having got contaminated with moisture.
The one thing I do notice is that there is a mixture of particle types in there, and the larger darker particles can tend to separate from the smaller lighter ones. If you just hold the open tub and gently move it from side to side, you can see them grouping together. I think this caused the composition of the mixture to change as I got further into the tub, and I'm trying to avoid that this time by every now and again turning the tub upside down (with the top screwed on!) and gently shaking it a bit, to try to reverse the settling that will occur from normally moving it about when upright.
It sounds like the new manufacturing process might help prevent this separation, though.