I think there may be many songs of this style that clashes with the anime, but one that comes to mind is Life is Cider which is about the ED of Wonder Egg Priority, the OP is quite slow and kind of sad but then they come and place an ED so happy and with party or festival rhythms hahaha, all very shocking when you're watching such a sad anime that touches on issues such as child suicide by different types of abuse.

also happened to me with the OP of Gokushufudo, a music with a somewhat strong style and like Japanese Metal, only to see that the most epic battles and scenes are those of Tatsu fighting against a stain on the kitchen floor that does not want to leave hahaha.