TYPO3 Core

I can confirm this. Happened on an upgrade to v12.
We have 2 menues, which generate the same menu items, but with different ATagParams (= different CSS classes).
The second menu is rendered with the CSS classes from the first menu.

How to reproduce:
- Create a styleguide Frontend tree
- Add this TypoScript:

page.2000 = HMENU
page.2000 {
    special = directory
    special.value = 740 # insert your pid of the Styleguide Frontend root page

    1 = TMENU
    1 {
      NO = 1
      NO.allWrap = <li class="nav-item">|</li>
      NO.ATagParams = class="nav-link" 
    }
}

- Open the frontend and inspect the menu

Expected: The menu items have the class "nav-link"
Actual: The class "nav-link" is missing

The first menu, which is rendered, is on the left side "mainNavigation".
Now add:

page.10.dataProcessing.10 >

Patch set 2 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/79575

Patch set 3 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/79575

We can confirm this too. If you have two menus on your page generating the same menu but with different ATagParams.
The AtagParams from the first one is used. But it this does not happen on all pages.

lib.testNavigation = HMENU
lib.testNavigation {
  1 = TMENU
  1 {
    expAll = 0
    wrap = <ul class="mainnavigation">|</ul>
    NO = 1
    NO {
      wrapItemAndSub = <li class="mainnavigation-item">|</li>
      ATagParams = class="test-navigation" 
    }
  }
}

lib.testNavigation1 = COA
lib.testNavigation1 {
    wrap = <nav class="navbar">|</nav>
    10 = HMENU
    10 {
        entryLevel = 0
        wrap = <ul class="navbar-nav">|</ul>
        1 = TMENU
        1 {
            expAll = 0
            NO = 1
            NO {
                wrapItemAndSub = <li class="nav-item layout-{field:layout}">|</li>
                wrapItemAndSub.insertData = 1
                ATagTitle.field = subtitle // title
                ATagParams = class="nav-link nav-link" 
            }
        }
    }
}

Patch set 4 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/79575

Patch set 5 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/79575

Patch set 6 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/79575

Patch set 1 for branch 12.4 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/79672