it's somehow difficult to give an answer because i dont have the data.
But you can try to add a distance parameter when using the connect method :
myRel.connect(cellList, polyList, 10.0)
but if it works with extending the raster size it may be just a bug
you can also increase the size when reading the raster entities :
let cellList = myRaster.readAll(shp.boundaries.buffer(100.0))