i loaded into mine too all my stuff is gone i had a life steal set that had 4 stars and was epic 1v.8 and a cruel weapon and shield on my main that was lv.12 i logged off got on after playing and got back on after a break and found all my artifacts went missing

Same here! I was playing this morning, game crashed and when I logged back in, all my artifacts were gone.

everyone to fix this mess delete your cache twice, yes TWICE (2nd time has to be after loging back in). If that doesnt work I'm affraid to say you must uninstall and reinstall the game. This glitch ran rampant in my clan thats how we figured out to fix it. Gl hope it works for all of you.

This has been happening to me randomly 1 or 2 pieces at a time. I just got the Day 87 login reward with  4 pcs of 5* Shield set and the chest piece is just gone. 

It seems to happen to me after I filter new items and close the window. I remembered that I went in to do my daily artifact upgrade quest and was going to put it on one of the new pieces but the chest was no longer there. I have only noticed it on PC and not on my android. 

Update 1. Clearing cache did not return this piece after logging in and resetting cache again. 

Update 2. Reinstalled and still no good.