Mine is that the useState hook is an actual plague on the entire React ecosystem. Regardless of your opinions of React, if you wanna use something then use it right.
As someone who uses Word at work, word online is severely hobbled, for example it cannot handle embedded documents. I'm glad they still have the word app
We also have other problems where our SharePoint librarian hasn't followed advice from the SharePoint Online team, but that, again, is user error