Hello ltjudd, great you managed to upload the pics!
One can see the issue you have described at the teal-coloured 310 kW arrow you marked. It is also visible at the brown-red 360 kW arrow underneath.
What I understand is that you are moving the grey waypoint up (C1) and down (c2), and as it snaps to the grid, the horizontal segment of the arrow either slightly goes up, or there is a slight downward slope.
First idea (although not the one I recommend!) would be to switch off the option 'Snap to grid'. In this case you will be able to move the grey waypoint up or down pixel-by-pixel (use the cursor or the arrow keys on the keyboard, hitting key moves one grid step, use CTRL+arrow key to move by one pixel). You could then try to fine tune the waypoint so that the line stays straight up to where it bends downwards.
But there is a better way to do this: why do you need and additional waypoint here at all? I would remove the grey waypoint, and instead pull the yellow lug point on the arrow all the way to the right, so that it sits above the vertical segment of the arrow. The first segment of the arrow will stay absolutely horizontal, and only after the yellow waypoint will the arrow start bending downwards.
I have made a small example similar to yours, see the three screengrabs below:
The first image is the start situation, then I drag the yellow lug point all the way to the right, to make the yellow point sit on top of each other in a vertical line. As you can see, there is now no downward sloping middle segment of the arrow, as I have not added an additional waypoint on the arrow.
Let me know if you could achieve what you were looking for with this trick.