I have tried in several places in my area (in ROW) and cannot seem to reproduce the issue. Does this still happen for you in a completely different area from the linked location while in incognito mode?
I think this is going to be a Local Issue bug. I was not able to add a JB to the junction in the PL but I could a few blocks away. I then went back to the junction in question and was able to add one (I deleted it after testing)
NOTE: I refreshed the page and then could not add JB again.
If it isn’t reproducible everywhere, then it does seem like a local issue. I recently ran into two place that I could change all the details on except the name and shape. Some kind of corruption, might be the same issue here.
I’ll move this to the local issues forum, and if it turns out to be a JB bug then we can just move it back.