This can happen, especially in regions with a low amount of roads (like mountain areas). That is a side-effect of the way we generate roundtrips.
What you can try is to reduce the avoidance of the same road from 2 to 1. I don’t expect that this will resolve the issue, but might make it less extreme. This requires a Kurviger Tourer membership, you can try this for 7 days for free to see if it helps or not 
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The other option is to change the route manually or to disable “avoid using the same roads twice”.