Sketchup is known not to generate correct STL files for 3D printing.
You can try to repair the file with an online tool like Netfabb, but in the long run it is recommended to switch to another program.
Cura 4.4.0 not slicing design
Some people swear by sketchup and 3d printing but they all know everything in this article. I suspect you only need to worry about the "reverse faces" discussion. Please at least skim this article quickly if you must use sketchup:
Recommended Posts
flg01 0
Same situation, a stl generated from Sketchup 2017. It looks fine in prepare view and incomplete in preview after slicing.
Link to post
Share on other sites