base:block has no corresponding route

Problem/Motivation

When downgrading a user from Administrator to a lower role, he gets a WSOD and can't use the project anymore. Clearing caches and rebuilding access permissions doesn't help.

Backtrace:

UnexpectedValueException: base:block has no corresponding route. in Drupal\Core\Url->getRouteName() (line 567 of core/lib/Drupal/Core/Url.php).

admin_toolbar_links_access_filter_filter_non_accessible_links() (Line: 52)
admin_toolbar_links_access_filter_preprocess_menu()
call_user_func_array() (Line: 287)
Drupal\Core\Theme\ThemeManager->render() (Line: 433)
Drupal\Core\Render\Renderer->doRender() (Line: 204)
Drupal\Core\Render\Renderer->render() (Line: 118)
Drupal\toolbar\Controller\ToolbarController::Drupal\toolbar\Controller\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 119)
Drupal\toolbar\Controller\ToolbarController::preRenderGetRenderedSubtrees()
call_user_func_array() (Line: 101)
Drupal\Core\Render\Renderer->doTrustedCallback() (Line: 788)
Drupal\Core\Render\Renderer->doCallback() (Line: 374)
Drupal\Core\Render\Renderer->doRender() (Line: 204)
Drupal\Core\Render\Renderer->render() (Line: 285)
{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 286)
toolbar_get_rendered_subtrees() (Line: 297)
_toolbar_get_subtrees_hash() (Line: 168)
toolbar_toolbar()
call_user_func_array() (Line: 426)
Drupal\Core\Extension\ModuleHandler->Drupal\Core\Extension\{closure}() (Line: 405)
Drupal\Core\Extension\ModuleHandler->invokeAllWith() (Line: 433)
Drupal\Core\Extension\ModuleHandler->invokeAll() (Line: 81)
Drupal\toolbar\Element\Toolbar::preRenderToolbar()
call_user_func_array() (Line: 101)
Drupal\Core\Render\Renderer->doTrustedCallback() (Line: 788)
Drupal\Core\Render\Renderer->doCallback() (Line: 374)
Drupal\Core\Render\Renderer->doRender() (Line: 446)
Drupal\Core\Render\Renderer->doRender() (Line: 204)
Drupal\Core\Render\Renderer->render() (Line: 479)
Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 83)
__TwigTemplate_7a8aff35746c404ed4bab73dd72bd985->doDisplay() (Line: 405)
Twig\Template->displayWithErrorHandling() (Line: 378)
Twig\Template->display() (Line: 390)
Twig\Template->render() (Line: 55)
twig_render_template() (Line: 384)
Drupal\Core\Theme\ThemeManager->render() (Line: 433)
Drupal\Core\Render\Renderer->doRender() (Line: 204)
Drupal\Core\Render\Renderer->render() (Line: 162)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 163)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse() (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray()
call_user_func() (Line: 142)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch() (Line: 174)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 81)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 58)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass() (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 50)
Drupal\ban\BanMiddleware->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 23)
Stack\StackedHttpKernel->handle() (Line: 718)
Drupal\Core\DrupalKernel->handle() (Line: 19)

Any ideas?

Switching the user back to Administrator makes the error go away.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes