I get this sometimes as well, it is definitely not to do with lag between client and server as other responses and ping are very decent. Server lag as stated by the previous commenter seems a potential culprit.

I thought this happened to me at one point but it turned out that the rags had just fallen on the floor (because my inventory was full). Sometimes however due to another bug (already reported by someone) server lag can mean that you don't see it on the floor straight away. So give it 15-20 seconds and it should be on the floor by then.

Confirmed. Used purification tablets on multiple servers and no matter what they always get ONE use, after that they disappear. It doesn't matter what percentage of tablets are left either. One said 90% and in the description 9 uses remaining but still only one use. I've tried dragging it directly from medic kit to water and from medic kit to inventory to water and it doesn't make any difference. This bug is making it much harder to have clean water.

I've also tried it with both canteens and water bottles, same effect.

Just another note which the person above has reminded me of, real life unedited photos of night time looking the way you want it (this goes for everyone, not just OP) would probably help a lot in persuading devs to change all their night time shaders.

Even though the image shown of potential night time looks lovely it is sadly unrealistic. We would never be able to see that lovely blue colouring on the backpack in a lighting situation such as that. It would look cartoony. I think Telltale games modify colours like this when it's dark in their games. It's a lovely colourful night time but not something that so far would fit in well with the rest of DayZ.