The big rat could be a pregnant one & hungry for nourishment. Hope you can catch it. Sounds like you have more than one rat ~ not surprising ~ they can breed as young as 3 months old. Weird that it's in a stall? Probably scoping out the territory discovering droppings from the other rat you video'd.
Wish I could loan you one of our Kensizer's just to see if it would work capturing your particular species of rat. They have such sensitive ears I'm thinking they may be put off by the energy emitting from your zapper battery. We can't sense energy but they have a super 6th sense.
Comes in 2 sizes... we got the smaller one to trap a little squirrel & were surprised when it caught a rat instead. It's been set out for rats all the time now. Some weeks nothing & other weeks anywhere from 1 to 3 rats.