You probably had a “Discontinuity” in the flight plan.
Check through your plan in the MCDU either before T/O or while airborne.
It will state that if it is there.
If a discontinuity is there, you need to remove it using the CLR button
I was doing all the right things and moved down form FL20 down to 4500 ft. Everything was being managed by the FD. However, this appeared so I have no idea what happened
When I saw that the FP was disrupted I had to fly it back on track. It picked up the glide slope but only when I took it there. Does this make sense
I can’t get it to replicate that no matter what I do!
I don’t think you did anything wrong.
IRL sometimes weird things happen as well.
My best guess is something in the planner went wrong.
Ensure you are using low or high altitude airways in the planner, and ensure you have an arrival and an approach selected in there.
If you see it happen in advance, you could delete one of the waypoints on eithe side of the missing stretch using CLR and that may join the route back together.
Otherwise, when you passed the last waypoint of the solid line, use DIR (Direct to) and select the proper next waypoint that is then displayed.