My cobalt Katar and death box disappear

In recent week I did not use the cobalt katar in the game , but when I checked my warehouse, I found that it was missing in the warehouse. All the skins I bought during the series of  colleaction activities are still in my warehouse, but my cobalt Katar and death box are missing, I want to know whether it is a bug in the game or some other reasons. I hope you can help me answer my doubts.