(I have no idea what component this would belong to.)
I discovered that breadcrumbs were being built twice for a page when the breadcrumb block was present and using schema_web_page to add Schema.org markup for breadcrumbs. This caused Facets to alter the system breadcrumbs twice.
\Drupal\Core\Breadcrumb\BreadcrumbManager::build should contain some form of cache for duplicate calls to itself to prevent duplicate breadcrumb calculations.
Postponed: needs info
11.0 🔥
render system
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
This came up as the daily BSI target.
Wonder if we could steps to reproduce this? I see it's using CacheableMetadata() which was added in 🐛 BreadcrumbBuilder::applies() mismatch with cacheability metadata Active maybe that addressed the issue here