Any chance the profile you were using had the "snap to nearest road" option turned on? If that option was on for the profile then that would be why it jumped to the nearest road.

I've had the nautical navigation work fine when canoeing on rivers and streams where you're following linear features on the map. What it lacks is the ability to plot a sensible course across a polygon of open water.

OsmAnd has the annoying quark of suggesting that I drive off my retaining wall, through some woods, and then across some wetlands, in order to get to the road behind my house, rather than directing me down my long driveway to the road a little further away. This is because the driveway is marked as private in the OpenStreetMap data, because it is private. Obviously I know to just go down my driveway, but anybody trying to get directions to my house would be sent to the incorrect road behind it and then just abandoned. I contacted the OsmAnd folks and was told it was an OSM problem. But other apps using OSM data don't have this issue. I gave up with OsmAnd after that.

I use osmand for privacy but I think it just emphasises main roads. In Melbourne it always suggests turning off cemetery road west because it doesn't know it's congested and will get me stuck for 20 minutes. And there are some missing slip roads. And navigation constantly fails to start. I wonder, how difficult is it to make minor edits to the map data?

If you lower max speed for your chosen transportation method osmand will alter your routing very significantly