Looks like chewed by something. Some of my neps have leaves chewed by jap weevils (or at least they looked like it) before it's fully formed, while they're still tender and soft (sounds yummy). After the leaves fully grown, they have all type of weird looking damages / holes. Sometimes the wound get some infection and rot a bit.
Maybe you can find the culprit if you randomly check on your plants in the afternoon and evening. After found the culprit, you'll have enjoyable time putting it into the pitcher or VFT.
Just to share my experience (and cruelness)
