So I did some more research and found out why the HOV onramp was a Parking Lot Road (so Waze will not give users that route, but will not consider it an error if they use it.) So, I changed it back. I also moved it farther North (away from the main lanes, in order to reduce the chance that Waze will 'snap' users to it.
More importantly, I noted that the segment between the Fair Oaks HOV onramp and the Marengo Ave onramp had different direction properties than the rest of the 210 segments. Specifically, the native direction of that segment was East to West. According to the documentation, this shouldn't make a difference, since it had its direction set to "One way (<--)" and the other segments had direction "One way (-->)." But, my computer engineering and programming background tells me that this is much more likely to be the cause of the issue than anything else I have noted, so I disconnected the segment and turned it around so that it's native direction matches the segments on either side of it. I checked the directions and connections to make sure everything matched, before I saved it.
I will post after the next time I drive the route.
Cheers, Dudley Sirius.