TYPO3 Core

Please post your Site configuration as well.

base: /
baseVariants: {  }
disableStaticFileCache: false
errorHandling:
  -
    errorCode: '404'
    errorHandler: Page
    errorContentSource: 't3://page?uid=50'
languages:
  -
    title: Deutsch
    enabled: true
    languageId: '0'
    base: /
    typo3Language: default
    locale: de_DE
    iso-639-1: de
    navigationTitle: ''
    hreflang: de-DE
    direction: ''
    flag: de
  -
    title: Englisch
    enabled: true
    languageId: '2'
    base: /en/
    typo3Language: default
    locale: en_US
    iso-639-1: en
    navigationTitle: ''
    hreflang: ''
    direction: ''
    fallbackType: strict
    fallbacks: '1'
    flag: en-us-gb
rootPageId: 1
routeEnhancers:
  NewsPlugin:
    type: Extbase
    extension: News
    plugin: Pi1
    routes:
      - routePath: '/'
        _controller: 'News::list'
      -
        routePath: '/{news_title}'
        _controller: 'News::detail'
        _arguments:
          news_title: news
      -
        routePath: '/{page}'
        _controller: 'News::list'
        _arguments:
          page: '@widget_0/currentPage'
    defaultController: 'News::list'
    defaults:
      page: '0'
    requirements:
      page: '\d+'
    aspects:
      page:
        type: StaticRangeMapper
        start: '1'
        end: '100'
      news_title:
        type: PersistedAliasMapper
        tableName: tx_news_domain_model_news
        routeFieldName: path_segment
  CoursePlugin:
    type: Extbase
    limitToPages:
      - 44
    extension: MyExtkey
    plugin: Myplugin
    routes:
      -
        routePath: '/{number}'
        _controller: 'Myplugin::detail'
        _arguments:
          number: number
    aspects:
      number:
        type: MypluginValueMapper
  PageTypeSuffix:
    type: PageType
    map:
      sitemap.xml: 1533906435
routes: {  }

I believe the problematic code is in the RedirectService, Lines 67-69:

if (!empty($allRedirects[$domainName]['flat'][rtrim($path, '/') . '/'])) {
    $possibleRedirects = $allRedirects[$domainName]['flat'][rtrim($path, '/') . '/'];
}

Georg Ringer wrote in #note-5:

IMO this is not a bug. you could use https://packagist.org/packages/studiomitte/redirect2trailingslash to redirect to the version with slash.

is that ok for you?

That would be the opposite of what I was trying to accomplish.
If I remember correctly my use-case was: I have a page with the URL "/somepage". Some external page has a link to this page, but they link to it with a trailing slash ("/somepage/") and I want to create a redirect to the url without the slash.