So was the razor sharp and the two planes of the bevel meeting at the 4K? It sounds like it wasn’t. Look at the edge straight down with a strong light and magnification. If you see shiny spots, the bevels are not meeting completely and are not set.

I believe it is common to not use a low enough grit to set the bevel or do enough laps at higher grits if that is all you have. Whatever you use, it must be sharp, and the bevels meeting before you go to higher grits.

I too, would recommend a 1K stone and learn to recognize when the bevel is in fact set. One of my best purchases has been a 600 grit stone that makes bevel setting quick and easy, then a 1K. Once you can set the bevel then you can experiment with a finishing stone, otherwise you are just grinding metal unproductively. Lightly dragging a Q tip along the edge, you will feel if it snags on a chip or unsharpened area.