I generally check bites starting at 6 weeks or so. However, when I checked my 4 week old litter, I noticed several had some degree of overbite. Some quite a bit and others only a little.

Does anyone know if this is just a usual stage for 4 week old pups just starting the weaning process?

I would not worry about it one bit. even if its over at 8 weeks I find that 9 out of 10 times its scissor at 6 months.

When I checked my puppies at that age one bitch had slightly overbite... she even had slight at 8 weeks.. now at 4,5 months as her front teeth are coming in she has normal bite... I feel it's even a bit tight scissor bite... so I wouldn't worry at this point!
Good luck with your puppies!!