It displays "null" both in regular listings and in featured snippets. Example: newbielink:https://nimb.ws/Kr9dgR [nonactive] and newbielink:https://nimb.ws/kNXAyf [nonactive].
When I checked it in the Structured Data Testing Tool it showed @id websiteuURL/null . At the same time, another website we own, that displays the path correctly in the SERP, shows websiteURL/#breadcrumb - newbielink:https://nimb.ws/BhbLPU [nonactive]
Another difference I found between the two websites was a plugin (activated on the website with the wrong breadcrumb)- Surbma | Yoast SEO Breadcrumb Shortcode.
Also, we have Yoast active on both. But probably on the website with the issue, it takes the data from the plugin.
Additionally, we have a Tag Manager tag for Blog breadcrumbs on both websites. However, I'm not 100% sure whether the breadcrumbs structured data is powered from the GTM or from the Yoast plugin or from that additional plugin (on the website we have it).
So, we first disabled this plugin (Surbma | Yoast SEO Breadcrumb Shortcode), then paused the GTM "Blog Post Breadcrumbs" tag.
Now, when I test the problem, the blogpost in the Rich Results Test tool, it shows all right-
websiteURL/#breadcrumb ( newbielink:https://nimb.ws/SJsbIU [nonactive])
I submitted the blogpost in the SC, so Google can detect any new changes. This was yesterday and I also edit the metas a bit. Today the metas are updated, so Google crawled the website, but it still appears with "null" in the SERP. Also, this "null" is nowhere to be found in the HTML when I check the page source, not before the changes, not now. Only in the Structure data testing tool.
So, any ideas? Should I wait more for Google to change the SERP appearance or probably the problem still exists? I can share the URL in PM if needed.