Hi @simongman,
Thanks for confirming those details. Since the issue only appears on-screen and not in exports, it may be related to how Illustrator is rendering the display. Could you try toggling the GPU Performance setting under Preferences > Performance and see if that changes anything? If the issue still shows on the screen, a sample file would be really helpful so I can share it with the product team for further investigation.
Let me know how it goes.
Looking forward to your update.
Abhishek