Hi @Anonymous
I believe this was caused from a design change with the toolbars in 2018.
It's possible as well it may be due to the image size of the icons which is why some of the icons scale a bit better than others.
While this isn't a bug or a critical issue, I highly recommend posting this on the Maya Idea Board!
This is a great place for the community to share ideas or feature they want to see in the future of Maya and this board is regularly checked by the dev team!
Please let me know if this information helps or if you need any more assistance!
If one or more of these posts helped answer your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.
Kudos are greatly appreciated. Everyone likes a thumbs up!