We are not able to view any imported geometry within Creo Illustrate 8.1.
Previous actions that worked involved changing the Filters settings.
This worked in Illustrate 7 but does not in our current version.
I can only suggest you contact tech support as without knowing exactly what type of data you are importing and what might have changed in your setup outside of Illustrate, it is impossible to comment.
The only thing I can say is that no changes have been made within Creo Illustrate in this area.
Tech support should be able to help investigate the issue properly.
"Open a Support Case": https://support.ptc.com/apps/case_logger_viewer/cs/auth/ssl/log