Ok, I'm not sure if this is already reported but I'll mention it anyway. there's a bug(?) where (I think) the blue coin somehow counts towards the combo.
The reason why I believe this is the case is because during my playthrough, I've made a conveyer belt system that goes from the start all the way to the end for automatic shredding. but then something happened and I start gaining a TON of combo, I think I went up to 6500~ something combo, and it cause the game to lag out.
I don't think it's any of the item that goes into the shredder that cause it to freak out because I was cleaning up the area and one of the item cause the conveyer belt to clog up, so whatever it is that causes the shredder to give me tons of combo isn't part of the random stuff in the office (like the potted plant or chairs).
The only logical conclusion I could make is the coin that piled up high causes the newly spawned blue coins to fall back into the shredder, which counts as a combo and spew more coins due to the upgrade which falls again and increasing the combo to produce more coins.