Illustrator Render

HI @GRcom,

We are sorry for the trouble. Multiple users have reported this. In addition to the steps suggested above by @Bill Silbert, would you mind trying resetting the Illustrator preferences?

If that doesn't help, would you mind sharing a few details along with the one asked by @Monika Gause:

• The exact version of OS & Illustrator
• Small recording of your whole workflow demonstrating the issue. It would be really helpful for us.
• Share the download link to the sample file in which the issue is replicable.
• GPU make & model
• Screen resolution of your display
• External monitor(s) make & model if connected any to your PC.

We are here to help. We just need more info.

Thanks & Regards,
Anshul Saini

Try turning off GPU Performance in the Performance section of your Illustrator preferences.

Some people have reported similar issues.

Which hardware do you have installed?