Saving as STL removes "holes" in objects


I’m trying to create objects to 3D print and have noticed that a hole on a surface/through the model becomes covered when saving as STL.
The hole is still visible in “x-ray” mode in the slicer.
I have tried two different models, made it as a component, reversed faces and all other thing I can come up with.
I have also tried opening the STL file in Blender to check if it was a problem with the slicer but it’s not.
Untitled.skp (91.2 KB)

There appears to be something wrong with the exporter.
As a workaround you can scale the object up by 10, download the stl then scale it down in the slicer.