Old routes are usually out of sync with your current global Tsection.dat file.
Update the route to current Tsection.dat before editing in TSRE or disable TDB editing in settings.txt.
Otherwise TSRE will destroy the route track database.
Yes, it won't work because I didn't know that it is allowed by MSTS. I will look at it later.
If you agree, then I will move this topic to feature requests or bugs.