I know it's moot since null elevations have been disabled in the latest release, but FWIW I was seeing the issue with or without JNF enabled. I didn't try every kind of edit, but with JUST Validator installed it had the same null elevation issue if I renamed a segment (changing turn restrictions didn't trigger it though).
I also agree that I think it was just a cosmetic display issue. Like SuperDave I could refresh the map data and all the elevation values were correct. I had to take it a further step because even though I knew the values were correct, the segments were still highlighted. The highlighting would go away after I selected/deselected the segment or did a full chrome page refresh. Minor annoyance, but nothing critical.
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