The Aqua Coaster and Honu Slides are open for EPA, which are in River Village. So the area should be open to find seating. The best shade spot in that area is a small covered structure that’s not shown on the map, but here I circled in red where it’s located:
Hi - did you also post about another unmarked shaded spot on the left hand side of the park? I saw the post yesterday but now cant find it. (Failed to bookmark it, like a fool). I think it was a reply to a similar recommendation from @darkmite2 about his favourite spot.