Hi, 

I was getting the same issue when customizing. So I decided to isolate the problem by selecting items one at a time and saving, when customizing.

I found two specific items I own, that when I try to equip and save gives me that error.

Inner Top > Aquatic Standard Tee (just released today)

And

Inner Top > Snow Leopard Tee

No other item I have will cause this error when it is equipped and you try to leave customization. 

Please solve this issue, I would really like to use these  

Thanks