Sorry for late reply, notifications went into junk. I didn't see the fill voids option, I'll check that out, but I doubt that's it. It's not related to importing objects, it's just that I'll notice perfectly square holes missing and any attempt to manually fill them will just make more randomly appear. At that point the whole scene is just unusable and I have to revert.
For a while now, I'll dip my toes into 3d coat as it's a very powerful tool, but is without exaggeration, the most buggy piece of software I've ever used in my 20 years of using graphic software. The biggest gripe I have is when holes appear in the voxel mesh at random. And it's not fixable, you just have to start from your last save point. I'll try the software out every now and then to see if newer versions have fixed the bug but each time it's still there. Does anyone know if this issue has been fully addressed and fixed in the most current versions?