utility classes not added to the build files

[x-o1d]

What version of Tailwind CSS are you using?

3.1.6

What build tool (or framework if it abstracts the build tool) are you using?

NX

What version of Node.js are you using?

16.1

What browser are you using?

Chrome, Firefox

What operating system are you using?

macOS

Reproduction URL

The behavior of the build system is unpredictable and erratic and cannot be consistently reproduced.

Describe your issue

classes like ml-auto/rounded-XX are sometimes in the build but sometimes not in the build.