I suspect the missing assets are probably updated versions of the KUID's used to build the original routes. There are no additional items in the merged route only those from the original routes.
There is certainly a need for a better way to get the latest version of assets into a route to avoud this problem.PG
A difference between 10 and 12 is in the disappearance in 12 of bridges at various places such as the Richmond river at Casino and the river northern end of Lismore. The Engine Complex part 7 loco shed in Casino loco depot is missing but the rails under the shed are there.
There was a Microsoft auto download upgrade a couple of days a ago and the problem of disappearing sheds and bridges appeared. I don't have proof as I don't have screen shots of before and after the MS upgrade but I am pretty sure I drove trains through the Casino area without missing bridges before the MS upgrade, so if anyone who has not installed the MS auto system upgrade could check this I would be grateful.
Also, the NR class locos seem to be a problem in tz12. Colour OK if close to it but only shows a black loco if viewing from a distance.
The bridges, loco shed and NR locos are still ok in tz10 after the MS upgrade.
As Pete said, I assume it probably needs updated TZ 12 versions of the KUID's used to build the original routes.
The quick fix is each of us to replace our own bridges with modern versions from the TZ 12 default list. In the real world the railways would eventually replace these bridges with modern stronger capacity versions so TZ12 users are just a bit ahead of the real world.
We are using Direct X here, if that makes a difference.