I've been working in Blender for some time, so I have experience with exporting stl from it with exact size and I had no scale issues with slicing.
But today cura showed a strange thing.
These are 3dBenchy and a stretched cube which are supposed to have 45mm height, also "boundary boxes" are turned on to show that there is no flying geometry.
And if I scale the ship inside the cura it will look like this
Does anyone know if I screwed up the model somehow or can it be considered as a bug?
Converted comment on OP to answer:
The comment links to a question on SE.Blender; the answer that led to the solution is quoted below.
The STL exporter doesn't take Scene Scale into account. Import your STL back into Blender (it will have the same size) and drag Scene Scale up back to 1.0, and you'll see how the cube grows relative to the grid.
1 Blender unit equals 1m, but STL seems to assume 1 unit as 1cm.
If you want 1 unit to be 1mm, set Scale on STL export to 0.1 and Scene Scale to 0.001 to make it match the output scale in viewport.
Note that the STL will be 10x smaller if you re-import it into Blender!