Hi Renata, welcome to our community. Feel free to Introduce yourself 
if you’d like!
This seems to be a bug on our end, and for us to resolve it we need to be able to reproduce it.
I’ll send you a Google Drive link with a folder where you can upload your model for us to test with, happy to sign an NDA too if needed.
In the meantime, you could try unselecting a few objects and seeing if that works, I think it might be failing to convert some specific ones.