Is it kept outside? It looks like it was chewed on.

tj

insect damages seams to be the most likely cause and yet the tip seams as if the edges have some ugly dull green mush edging, hum.......

If it sits on the grass to water and drain then sneaky snails could have snuck in within an hour. And caterpillars are laid as eggs on plants by flying insect adults.

It does look like damage from one of these munchers though. Kind of a relief, I believe. Do you have lettuce or even potatoes? You can lay them on top of the media to try to attract snails then squish and flush them.

Also, if you repotted it and havent had it long its entirely possible there were snail eggs on the roots and they hatched after you repotted. Some people spray roots with hydrogen peroxide to kill snails and their eggs but I'm not sure how a fern would handle such treatment.