This seems like a fantastic plugin!
I too am having issues with 1.1.5 on Mac OS 10.12.6. with Sketchup 2017 Make.
A poster back on page 6 had the same issue I am having. I dont know if I can post images here or not as I dont frequent the site enough. His earlier post had this...
https://sketchucation.com/forums/viewtopic.php?f=323&t=71951&start=120#p656540
Im getting the same and was wondering if its an OS issue. I downloaded the most recent version of ASSIMP thinking I might need that. Do I? Couldn't figure out how to install it anyway. 
Would love to get this sorted to be able to play around with this and put it through its paces. Thanks for any insight.