Help with a whatsapp problem

Every so often like once a month or once a week a collection of about 50 photos from an old whatsapp chat reappear in my phones gallery as the most recent photos and I have to go through and delete them all every time this happens.

The photos are always the exact same every time.

It was happening on both an old phone and my new phone.

Why is this happening? Is it some kind of archive issue? How can I stop it from happening?