So one problem with large isometric maps is that the map's boundaries is still an axis-aligned rectangle, with the maps corners intersecting with the center-points of each of the rectangle's sides. This leaves a triangle of "empty space" in the corners of the rectangle. In cases where the map node's position is 0,0 the width and height of the screen may fall entirely within that empty area of the tilemap, particularly if the map is large. Hence you can end up seeing nothing (initially) even though everything is okay. I should know that yet I failed to realize this for quite some time, wondering why my fixes still don't work and position updates cause tiles to disappear.
To illustrate, imagine the draw call, fps labels being the screen's area. In that case you would see nothing but black space but the tilemap is still drawing correctly. You just need to offset the map move some of the tiles onto the screen area.
I made a small 10x10 version of the tilemap to avoid having this problem again.
Thankfully that wasn't the only problem, the bigger issue was renderSize not being implemented and once implemented they caused too many sprites to be cut off from the screen, hence nothing was visible (again in combination with the above issue).
I'll send you the updated sources by email.