Damaged tape with skinny dyneema tape for comparison.

any expanation as to how it happened?

Apparantly the rope rubbed across the tape in a fall and melted partially through. It was noticed after stripping draws out of a redpoint project so unable to tell the exact circumstances of rope & quickdraw orientation, but it was normal use and the falls were unremarkable. Adds a new slant on nylon vs. dyneema debate - difficult to say whether the outcome would be different on a skinny dyneema sling but obviously there's more material in a fat nylon tape to absorb damage.

ahh, yes, i can understand that.

Yes, and Dyneema has a much lower melting point.

Put some gaff tape on that then.