why cant i make something hollow?

[Adamsk1 0]

as you can see the bottom of this thing i have wont correctly load in a way where it is hollow, i have all the faces correctly defined as well, anyway around this?

 

[Dustin 160]

Will need a UltiMaker Cura project file for anyone to be able to help you with this.
guide: https://support.ultimaker.com/s/article/1667411030205

[GregValiant 1,342]

Yeah, a project file is necessary.  All those "Outer Walls" that are showing on the bottom of the tall model aren't right.

 

Make sure "Remove all Holes" and "Make Overhangs Printable" are turned off.

[Adamsk1 0]

here is the file i think, i tried the remove all holes setting and it did clean it up, but didnt make it hollow. anyway have at it

 

CE3E3V2_beck with base.3mf

[Dustin 160]

Well theres your issue, your model is VERY broken.. 
Not sure why you got no error popup.. but those blue and purple dots at the bottom are very bad.

Additionally the red surface on the top is odd.. this model appears to be inside out and corrupted. 

Read more here: https://support.ultimaker.com/s/article/1633018228456

[GregValiant 1,342]

One has been repaired (MS 3D BUilder).  It did not have a hollow base...it just looked hollow.