The Update Announcement Thread (at
https://forums.auran.com/threads/trainz-update-announcement-sp5.179952/) is full of messages about this "bug" in the update. There is a simple solution provided by one user
@JCitron
1. Close Trainz.
2. Go into Content Manager.
3. Search for your tracks using category track.
4. Open up all your track for editing -
(Select all - click on one and press CTRL+A and then Right-click and choose Open for editing)
5. Submit all DLS track OR
6. Revert to original all built-in and DLC track.