A similar problem just happened:
https://community.adobe.com/t5/illustrator-discussions/the-welcome-screen-layout-is-confusing/td-p/14047747

Same problem.

The solution by Charu Rajput just doesn't work

Rama's process worked for me too.

Thanks for the clarifying help Griff!!! Worked perfectly!!!

If you're using a mac, your computer has two "Library" folders.

macOS > Library
macOS > Users > {computer name} > Library (but it's a hidden folder)

The "Caches" folder is in that second one.

You can get there by selecting the Finder menu item "Go to Folder" under the "Go" dropdown, then typing this address in there:

"~/Library/Caches/Adobe/"

From there, follow the steps that Rama noted above.

There doesn't seem to be Cache for Adobe in my Library Folder. I did restart the CCXProcess with no change to the problem.

As of MAY 16 This issue is no longer happening. Also, I didn't have to do any fix! Just opened it and was normal.
Somebody mentions a side question of the arc tool not working, I checked and it's still working in my program.
Specs: MacOS Catalina 10.15.4,
Illustrator 24.12
CC 5.1.0.407
CCX Process 3.6.2.5

When I try to click on the arc tool it selects but the function does not work.

I can confirm, that Rama's workaround does the job! Thanks so much.

Hi, try steps mentioned at below link.

https://community.adobe.com/t5/illustrator/home-screen-presets-icons-display-issue-in-illustrator-cc2020/td-p/11076227?page=1

Thanks

My experience was even more interesting. I saw the May 12th email alert with Rama's workaround this morning, but before I did any of it, I launched Illustrator to work on something real quick and the issue was already fixed. Moreover, I had a new splash screen letting me know what was new in the Illustrator update, even though the CC app says the last update was 15 days ago, and I'd been using Illustrator umpteen times since without seeing this "What's New" splash screen. Weird!

For the record, I’m no longer having this issue, but I followed the steps above [killing the process in Activity Monitor] and it cleared up a separate issue I had been having with Adobe XD. Thanks!

I would like to report that I followed the workaround that Rama has outlined 12 May 2020 and it works.

I'm on Mac OS Catalina 10.15.4, and when I launched Illustrator just now the icons on the home screen were oversize and not contained within their tiles.

Same, but for macOS Catalina.

The formatting is messed up on the startup screen (using: macOS Catalina)...

Same.

As of May 4th, the issue persists even though it is marked as "completed"... This fix is not completed.
...
Most current CCX process. Most current version of Illustrator and CC.
macOS Catalina 10.15.4

I am also running CCX Process 3.6.2.5 and still have this UI problem. (Oversize preset icons at Welcome screen.)

Not "Completed" as of May 4, 2020, with everything Adobe updated. I still have huge preset icons with:

iMac (Retina 5K, 27-inch, 2017)
Mohave 10.14.6
Illustrator 24.1.2
Creative Cloud 5.1.0.407
CCX Process 3.6.2.5