Clown Plecos are territorial. Some more, some less. My guess is, your pleco is currently trying to establish his territory and defend it. Your panda cories otoh aren't territorial, so they will enter your plecos backyard not knowing this is danger-zone. From experience I'd say they will also never learn this
Your pleco otoh will likely get more relaxed towards the cories as he learns that they aren't rivals.So as long as your pleco is just defending his yard I'd say it's fine. Cories can be very fast if they flee, so no worries. It helps to add some pleco caves so he feels safe. Also make sure that he can't see the entire tank from his cave. They usually just defend the parts of the tank that they can see.
Story: One of my clown plecos is on the more aggressive side and started to hunt down cories in the entire tank. Putting a big bristlenose male into the tank fixed this because the new fish replaced him as the alpha catfish. He still has his funny five minutes every now and then but the bristlenose will kindly remind him who the king is and who is not.