You didn't mention if it was raining when you closed the slides. If it was NOT raining, then ignore this answer. If it WAS raining, then it is likely that the rain, the water on the slideout roof, and slideout sides was drawn in as you closed the slides before the trip. It is unlikely that you would have seen this as you prepared to leave for the next location.
During the trip, all the water drained down from the slide roof and walls. The wiping action of the rubber seals doesn't catch all of the water, plus there are some gaps as the slides are closed until the slide seals itself tight against the RV wall.
We have had this issue several times, especially when it is raining hard when we pack up. Light rain isn't necessarily going to make this happen, but hard rain makes it more likely.
Maybe there is something different going on with your issue, but give this some thought if you can't find an actual problem