Wave models provide data as a grid, that very roughly matches with the shoreline. Windy hides the data that is on the land by the base map. And depending on the resolution of the model (GFS has a low resolution), the interpolation of the grid points, the zoom level, you get these small glitches, which disappear when you zoom in. If you want to know the forecasts of the sea state near the shore, so zoom in.
This picture from a wave model may help you understand what I mean along the sea shore.
In addition there are areas where swell is missing with GFS-wave model.