As cookie mentioned, it's most likely coming from the AC. Check your gutters. I kept finding a puddle on one of our slides while checking the slide tops for travel day, and I eventually figured out there is a small break in the gutter where it has to bend to conform with the slope of the roof. Water is able to work its way through the tiny crack and onto the top of the slide.
Could you give a little more information? Is the water on the top of the slide out or are you talking about water coming out the bottom near the jack? We have the same unit as you, 2018 RW427.
We had water come out the bottom before and it was because the inlet line at the hot water heater had cracked causing water leak. Also that is where your fresh water tank over flow is located. Look underneath the slide and you should see a short line extending from the frame a few inches.
If the RW was getting it's fresh water filled, it may be the overflow line is resting on the frame and running to that spot. If your hooked up to city water and it started leaking, it could be the same thing happening with an Anderson valve cartridge leaking.