quantity changes

[missida]

I have had a couple of episodes lately of items showing or changing to 0 in quantity/out of stock on it's own.  I thought maybe I made a inventory mistake.  Within the last week I redid my Quantity #'s & within 3 days  I had a group of items (all in the same category) mysteriously go back to 0.   Anybody have answers? 

[inhawaii]

Glitch?

Ghost?

User error?

I have never had this happen to me, but I have heard others sellers mentioning this happening to them before.