That is a long time to thump! I’ve never heard of a bunny thumping for hours. It seems like that could actually damage their feet/legs.
Rabbits thump when they are excited, mad or frightened. Do you think that there could be anything frightening your rabbit? I don’t know where you live, but it’s winter here, and we sometimes get a mouse in the house in the winter. A mouse might be attracted to any food in a rabbit’s cage. Do you have other pets that could be disturbing your rabbit? Are there any new sounds in the house (like from an appliance) or the neighborhood, or different smells in the house? Do you get up and observe him or try to calm him, and does that help at all? Is he still eating and pooping normally and acting normally during the day, and is in good health? Does he get plenty of out of cage time for play and exercise during the day? Is his cage a big enough size to give him plenty of room? Something must have triggered this thumping, even though you say nothing has changed for him.
I know this really didn’t help much, but maybe with some observation and detection work, you can figure out what started all of this.