**What caused the problem** I inspected your data. The problem is the geometry of your line. It's very weird. Vertices appear in a chaotic order: Start point (first vertex) of the line is somewhere in the middle, next few vertices follow the river, than it jumps to another part and continues there for a few vertices etc. **How to solve the problem** 1. [`Explode your line`][1]. 2. Select all features of the exploded line and [`Merge selected features`][2]. Than you can apply your label along the line where you want. [1]: https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html?highlight=explode#explode-lines [2]: https://docs.qgis.org/3.16/en/docs/user_manual/working_with_vector/editing_geometry_attributes.html?highlight=merge#merge-selected-features