Re: Serious problem with inventory disappearing

Check your valuables. You may have a ton of stuff like statuettes, figurines, malchite, etc. or even things you can turn in to Maive in haven or the other researcher in skyhold.

also check for requsitions that can be filled. (campsites, therinn in haven, or the other guy in skyhold)

make sure you turn in your creature items (yellow)....

make runes for your weapons (uses up your elemental essences and blank rune stones)...

sell all of the grey armor and weapon items, if you don't have or can't make better.

keep the purple and blue ones, and sell them to merchants, if you or your party members cant use them.

crafting items DO NOT take up inventory slots. schematics, metals, hides, herbs, elemental essences, etc.

also in the main inventory menu (on pc at least) you have to scroll down to get to the other catagories.... schematics, valuables, crafting materials, recipies, etc. 

and a.f.a.i.k. the total amount of non-crafting items you can carry is 90, through inquisition perks.