pickable objects disappearing (invisible) and reappearing on the world, how to fix?

It's normally glitched out since items are can actually float unless one of the items or taken or holded. This also occurs it it's appearance. I would recommend trying to take items instead of holding the items [if that doesn't work, take the item near it].

The problem with this in Skyrim is the physics engine itself, sometimes the items you place either do one of two things:

• De-spawn due to placement error whilst re-loading and implementing the game code (basically there's an original copy or code for each room and area, then there's a new copy based on what you alterd in the world, and sometimes the game gets confused and over-rides the new copy causing items to "disappear". It's an engine stability issue.)

• The game sometimes uses texture overlays instead of using physical barriers (it's easier) so the items don't actually "disappear", they fall through the maps visually perceived area. There are some mods for the PC that add more physical barriers under visual ones as a preventive measure. But other than that there is no resolve to this. It's something only the DEVs can fix.