@CharlieFox00 did you try with a fresh opening of the flight planner in a new and/or a private window?
I don’t know if you saw my posts, but I couldn’t replicate it once I stopped using the already open tab with the flight planner that I’ve had open for a few days now.
Although, the first time I used the flight planner, I had success with this very flight plan. It was the subsequent tries where I had issues.
Leave it to me to have even have found this with the one and only flight plan I have tried building with this tool.
My luck(?) is absurd.