Mortar wasp - sap does not work / split screen issue

So we are playing the boss fight with the mortar wasp and in the beginning it worked fine. I play Cody and use the sap to cover her up and then my partner shoots at her. However after once or twice going through this process it does not work anymore. On my screen (both May and Codys side) I see the wasp fully covered in that gelee and i keep shooting it at her. But on my partners laptop you cannot see it. So whenever she shoots at the wasp nothing happens. On her screen it looks like I haven't shot at the wasp even once. She is completely clean.

So that means we are currently completely stuck and don't know how to fix this. If anyone has an idea we would be grateful.

- Alex