If you find that either:
you can report them problem to the OSM community or fix the map yourself. OSM is an open-source project so relies on contributions from users to develop and improve the maps.
To make changes to the map using the OpenStreetMap editor you'll first need to sign up for a free account on OpenStreetMap and then login.
Then follow these instructions to edit the map:
You can also upload missing paths from GPS recording by selecting the "GPS Traces" option from the menu at the top of the page.
Changes to OpenStreetMap will take time to feed through to plotaroute.com - this can be up to 30 days but is usually much quicker.