I had gear equipped on 2 out of 3 characters. I used these 3 characters to rank up a 3 star character. All the equipped gear on those 3 characters was destroyed. No warning or anything. Just gone.

Note 1 set was a full set of purple 4 star rank 7 offense item i got from a chest.

Other set was also purple and maybe 3 star with rank 7. 

Cant really add any photos as the items were removed.