UPDATE:

This issue has been resolved by Apple in its latest Beta seed. Please join the public beta program of Apple here: https://beta.apple.com/sp/betaprogram/

Adobe Knowledgebase Article: adobe.ly/2rwbXVh
Adobe Internal Bug Tracking Number: AI-4208860
Apple Internal Bug Tracking Number: 34279339

Workaround 1: Disable GPU Preview
Workaround 2: Change the color mode of the document to CMYK.

This issue has been acknowledged by Apple and they’re working to fix it. To learn about their timeline or other details, please contact Apple Support:

support.apple.com/contact
apple.com/feedback
twitter.com/AppleSupport
Due to compatibility issues with some GPU cards, you may face rendering errors while zooming and panning your artwork, drawing with Brushes, and working with on-screen widgets such as the Live Corners widget and the Perspective Grid. These errors occur while you’re working on a document set to RGB color mode.

The following GPU cards are known to be affected by this issue:

Intel Iris Plus Graphics 650 1536 MB
Intel Iris Graphics 550 1536 MB
Intel Iris Plus Graphics 640 1536 MB
Intel Iris 550 1536 MB
Intel HD Graphics 515 1536 MB
Intel Iris Graphics 540
Intel HD Graphics 515
Put in the comments section if you have any more GPU that you believe we should be aware of.

UPDATE:

This issue has been resolved by Apple in its latest Beta seed. Please join the public beta program of Apple here: https://beta.apple.com/sp/betaprogram/

Adobe Knowledgebase Article: https://adobe.ly/2rwbXVh
Adobe Internal Bug Tracking Number: AI-4208860
Apple Internal Bug Tracking Number: 34279339

Workaround 1: Disable GPU Preview
Workaround 2: Change the color mode of the document to CMYK.

This issue has been acknowledged by Apple and they’re working to fix it. To learn about their timeline or other details, please contact Apple Support:

• https://support.apple.com/contact
• https://www.apple.com/feedback/
• https://twitter.com/AppleSupport

Due to compatibility issues with some GPU cards, you may face rendering errors while zooming and panning your artwork, drawing with Brushes, and working with on-screen widgets such as the Live Corners widget and the Perspective Grid. These errors occur while you’re working on a document set to RGB color mode.

The following GPU cards are known to be affected by this issue:

• Intel Iris Plus Graphics 650 1536 MB
• Intel Iris Graphics 550 1536 MB
• Intel Iris Plus Graphics 640 1536 MB
• Intel Iris 550 1536 MB
• Intel HD Graphics 515 1536 MB
• Intel Iris Graphics 540
• Intel HD Graphics 515
• Put in the comments section if you have any more GPU that you believe we should be aware of.

We are aware of GPU issues on few Intel graphics card on Macos 10.13. We are working with Apple and trying to get this resolved. The fix will be in graphics driver that macOS bundles.
Few users emailed us that they see this issue on their MacBooks that does not have Intel cards. The MacBooks that you are referring to actually do have an Intel card. These have dual graphics card and the bug surfaces when it switches to the low powered card. Disabling “Automatic graphics switching” in “Energy Saver” in System Preferences is a workaround on those machines.
If you have any other observations please drop in a comment or please get in touch with us at sharewithai@adobe.com or any of the other support channels – https://helpx.adobe.com/support.html .

Alternatively, you can also pass the feedback to Apple here : https://support.apple.com/contact or https://www.apple.com/feedback/

We are aware of GPU issues on few Intel graphics card. We are working with Apple and trying to get this resolved. The fix will be in graphics driver that macOS bundles.
Few users emailed us that they see this issue on their MacBooks that does not have Intel cards. The MacBooks that you are referring to actually do have an Intel card. These have dual graphics card and the bug surfaces when it switches to the low powered card. Disabling “Automatic graphics switching” in “Energy Saver” in System Preferences is a workaround on those machines.
If you have any other observations please drop in a comment or please get in touch with us at sharewithai@adobe.com or any of the other support channels – https://helpx.adobe.com/support.html .

Thank you for sharing your system information. Unfortunately at this time the only workaround is to turn off GPU

We are aware of GPU issues on few Intel graphics card. We are working with Apple and trying to get this resolved. The fix will be in graphics driver that macOS bundles.
If you are not seeing this issue on Intel cards please log a new bug or email us on share with ai (at) adobe.com
- Please remove spaces from share with ai and replace (at) with @

Please stay tuned for an update.

To investigate we need this information: Please share the Help menu> system Info content on the machine where this is happening.

Please share the Help menu> system Info content on the machine where this is happening.

Please share the Help menu> system Info content on the machine where this is happening.

We do not support macOS 10.13 for version 21.1. thre are two things going on here Apple may fix this in subsequent seeds or we will fix it in the next version of Illustrator. Expect macOS 10.13 support only in the next release of Illustrator