The 2 rules are the same rule listed twice:

- Generating index html...2 rules skipped due to selector errors:
  .form-floating>~label -> Did not expect successive traversals.
  .form-floating>~label -> Did not expect successive traversals.

>~ is obviously an invalid selector, however it doesn't look like that's ever actually used in the Bootstrap code. I've checked myself, and one of the bootstrap devs has also confirmed it twbs/bootstrap#39323. The base style is simply .form-floating > label while there are a number of styles in the format of .form-floating > [another selector] ~ label. It seems one of those intermediary selectors is being removed during CSS processing.

There is a workaround of disabled Inlining of Critical CSS, but of course we're then missing out on a possible performance improvement.

This was reported as an Issue with Angular CLI last year, but they indicated it is a problem with Critters: angular/angular-cli#25725 (comment).