I have two light switches in my kitchen adjacent to the entry ways (walk thru kitchen). I use to be able to turn off/on the lights at either switch, however now, both light switches have to be in the off posistion for the lights to be off. As I wrote earlier, it didn't matter what position the switches were to turn them off or on.
Most likely a loose connection has developed in the wiring at either or both switches.
Another possibility is that something failed internally in one of the switches.
Those "push in" or "backstab" wire connections (no screws needed) on switches and receptacles have a high likelihood of problems of this kind after several years.
When cleaning anything including baby diapers, it is better to sweep off or scrape off as much solid and semisolid material as you can first. (1) Less cleaning fluid or detergent needs to be used, (2) Less of a mushy mess which in turn means that bleaches or disinfectants will be more effective.