I've got a Garmin 500 and have tried running routes in the past. Seems on every one that I tried there'd be a turn it missed and areas that it acted like it was not getting a GPS signal. I really suspect it had too much going on and the processor was simply overloaded for that moment in time.

Routes aren't a big deal for me and I don't even try to use them anymore. I know where I'm going and if I don't then a view of a map before the ride or a look at google-maps on my phone quickly tell me what I need to know.

Not sure what this means toward your issue other than to say some users of Garmin, Lezyne and other makes of devices have various issues with routes too.

As others have mentioned, how you create the route, what site or software tool you use and even how you save and install the route on your device can make a difference.