This happens with any item that you craft. Including Guns. An easy example is to take the Trombone have it in your pack and already have another rifle in the slot such as a winchester. Then Assemble the Trombone and it will just completely disappear. Another way to do this is the reverse. Have a Trombone in hand with not enough space for it in your inventory and it will simply disappear completely.

In addition I know it happens with Sawing off the IZH8 as well. Not to mention other crafted items such as improvised backpacks etc.

Confirmed.

While he's got a good point here I can add some additional information.

It seems that it's not just Drinking directly from Pond/Well but also using the Water Bottle and Canteen. I experienced it most notably when using the "Drink All" Function. I gained only a little hydration compared to the amount that it seemed to think it filled up my stomach.

A direct example of the hydration to fullness would be this. It seems to fill my stomach just like it should if I "Drink All" the whole canteen at once but it only provides the hydration level of one "Drink" not a hydration level of "Drink All"

In addition I should note that Natural Water Pouches crafted from Tanned Leather seem to work fine but I'd need more testing to verify for sure, but I think I get full hydration from "Drink All" with those unlike with the other containers.

I wanted to add that on Stable this is still the case and that it won't cook with a Gas Stove either. Incase that requires an additional fix since the stove is different from the fire.

I've also gotten the error message several times. I'm not sure if it's the gun itself that is causing the error or the speedloader for it as after I ditched the gun I kept the loader and still had the issue on login.

I've had the same problem though dropping and requipping the item didn't resolve the issue for me. Also relogging didn't fix it for me either. I'll try both again next time though just to be sure.