Route snapping uses an external routing network, and a few trails that are visible on the map aren’t in that network — so the planner routes around them via roads instead. Workaround: tap the Routing button, switch to Line mode to draw straight lines along the missing section, then switch back to Hike mode to continue. If snapping draws straight lines everywhere on the website even in Hike mode, a firewall or ad-blocker (common on work networks) is likely blocking the routing service — try another network or the mobile app.