Of all the major maps available (Google, Apple. TomTom, OSM), HERE is the least reliable. As has been noted in several threads, the status of closed/open roads is continuously missed, out of date POI's remain on the maps for years, and unexplainable route calculations happen too often. Adding to the list, I recently found a HERE cartography error where sections of a road are actually in the wrong place.
In the nutshell, HERE is HERE, and none of these significant deficiencies are going to change. Realistically, MRA is too functionally married to HERE to simply change vendors. MRA is painfully aware of the situation, but their hands are tied and they have no other choice than to make to best of the situation.
Given the situation, as users of MRA, there are things we can do to somewhat mitigate the pain. The easiest is to perform all you your road status checks outside of MRA. Google and Apple provide accurate up-to-date road information that can easily be checked during route development. Additionally, if the HERE map won't let you route through a road that you know is open, and passing through that road is critical to your trip, consider using OSM as the base map. Unfortunately, this will only work if you're using a GPS instead of the NN phone app for route execution, but at least that choice is there for those it applies to.
There are many tricks-and-tips for HERE workarounds posted throughout the forum. Many are very cleaver. It would be helpful if all those could somehow be consolidated and documented in one place for reference. I think that would be about the best we could get given the situation.