In my case the floss caught on the sharp edge of the wireless charging coil pulling up the edge of the coil, butane cutting off the floss. I think the coil had been damaged by some previous repair, but be careful. After you pull past the first two adhesive strips, peek under the battery to make sure the floss is sliding over not under the coil. The coil doesn't look like a coil – more like a paper thin pad.

Can I make my own adhesive strips from 3M double-sided tape?

Can I make my own adhesive tape by trimming standard 3M double-sided tape to fit?