Hi H222
Unfortunately a bug in the SP2 release of TANE caused, in some situations, for the terrain to become corrupt in some parts of a route, returning to the '0m' height. This bug was not verified until after the SP2 release was made available. If the route was saved after the corruption occurred, then the corrupt data would have been saved to the route. In this case there is no way for the data to be repaired, as it has been saved with the corrupt terrain height information.
We have always recommended keeping regular backups of all content, in particular routes and sessions, as there is no way to guarantee that data cannot become corrupt (either due to a bug, or due to a crash, or other software interfering, or hard drive issues, or other potential causes of corruption). Either by making incremental saves, or by saving a regular cdp file backup of your route.
Regards