Glowfly Cocoons not formed by Great Leafy Stalks still count as Glowflies, meaning that they can be caught with a Bug Net, and moving too far away causes them to despawn.
Steps to Reproduce
Wait for a Glowfly to become a Glowfly Cocoons, then you can use a Bug Net to catch it. If you move too far away from the Glowfly Cocoons, it despawns.
This issue has been fixed in either a future version or updated in a previous version.