I could not yet reproduce that Assertion failure in line 12302 also trying several runs adding one worldspace after another. It might be that it only happens with a lot of mods or a mod that might have errors.
Use the latest beta version from this post. Nothing changed anymore in the particular code to the original problem in this thread, but you never know - always use the latest :)
Edited by sheson, 13 September 2017 - 04:59 PM.