Hey Peter,
We tried to trace the problem here in-house, but couldn't get to repro it. We have speedtrees in all the routes and surveyors etc. We even changed the Video settings between Open GL and Direct X graphics modes and tried to repro the bug in Nvidia and Amd machines.
Could you try changing the video settings between Direct X and Open GL and see if the bug still exists? Updating video card drivers and your OS (for direct x, etc updates) would be a recommended step as well. Check if you still have no speed trees in the built-in routes after doing these updates and post back.
Regards,
Sidds