The fact that you have two red arrows on the lever indicates that it is not correctly positioned on the junction. This can be incredibly fiddly to fix manually. Try using the Move tool in the Trackside section of the Track tab to slide the lever back and forth - it is moved into the correct position then the red and green arrows will appear.
If that does not work, and this can happen on curved junctions, then a more drastic solution is required.
Delete the junction (by deleting the track) and, if it is still present, then manually delete the lever as well (the Delete button). Then recreate the junction by joining the track elements together. This will automatically create a lever (the default one) in the correct position with both a red and a green arrow.
If you want to swap the default lever with a different one then delete the current lever and, after noting its exact position, select the new lever and then use the Add button to carefully place it in the exact same position.
Peter Ware