I'm pretty sure I have it figured out.
After talking to bigbear3764, the theory is:
(1) Map tiles in the live map have corruption that causes them not to download to the current client version
(2) The current live map tile generation process only generates new tiles when changes have been made.
(3) If you edit the area where the problem is occurring, it will force a rebuild of the affected tiles and fix the problem.
- edit the geometry of the affected road
- If the area is locked above your level, (1)draw in a new road. (2) save. (3) delete the road. (4) save again (I waited for the live map to be updated before steps 3 and 4 - others I've talked to did all 4 steps at once)
So far this has worked in all the areas I have had this problem.