Welcome to Pet Talk.

I haven't experienced this myself, so take it with a grain of salt... okay a BIG grain of salt. But one of our members had a similar problem last spring/summer where one of her cats started attacking another for what seemed like no reason. As I recall, the cat being attacked was starting to develop a health issue that changed her blood chemistry/smell. (At least that's how I remember it... ) So the pets who were chums previously -- well one of them didn't recognize the other anymore due to the odor difference. Once she began treatment, the problem went away fortunately. When you next take Leiloo to the vets could you check and see if this makes any sense in your case? (Or weirder yet, could Bandit be coming down with something that throwing his nose off?)

I feel like I'm babbling here. Good luck and with luck you'll get some good advice from some of the others. It is odd that Bandit has suddenly taken to attacking Leiloo. (Oh! Did the guy doing the mopping notice anything odd before it started??? Did one or the other get into the water/chemical solution?) The more I think about this, the weirder it sounds!