OSM is acting up. When I zoom in on Lake Lewisville, part of it disappears.
https://www.openstreetmap.org/#map=13/33.0966/-96.9950 (https://www.openstreetmap.org/#map=13/33.0966/-96.9950)
You should report it in this OSM-dedicated thread: https://www.aaroads.com/forum/index.php?topic=4420.0
I checked with JOSM and the whole lake is definitely there in the database, so the issue must be with Carto (the renderer used by the main site) not rendering the multipolygon in some tiles on certain zoom levels. (Zoom in more and it's there again.)