Help with missing or extraneous parts

Often when I upload my STL in Cura to slice I get an error message saying I need to fix my model. Some work fine and then randomly others won’t work. I use the exact same profile setting I save in CookieCad.
I am getting frustrated and need to figure out how to avoid this.

I attached a screenshot of the error message and a photo of how they print.

What i always do is before using the slicer I open it up in 3d builder and if there is errors it will fix it for me then re-save the file
3d builder is free

You should be able to ignore the error and print it as is. Cura will often complain but it should slice fine. Look at the slice preview, if it looks good there then there it is not a problem. Check if that missing area is in the sliced preview, (click preview in cura after slicing) if it is not, then the missing area is not due to that but another problem with your printer or settings.

Also, do not resize the cutter in Cura, it can cause issues with the blade, always size it in Cookiecad before bringing it into Cura.