False Soft 404s, Shadow Bans, and Old User Generated Content

[STDCarriers]

What are the best ways to keep old user generated content (UGC) pages from being falsely flagged by Google as soft 404s? I have tried HTML site maps to make sure no page is an orphaned but that has not solved the problem.

Could crawled currently not indexed by explained by a shadow ban from Google? I have had problems with Google removing pages from SERPs without telling me about it.

It looks like a lot of content is not ranking due to its age. How can one go about refreshing UGC without changing the work of the user?

[STDCarriers]

I solved most of the Soft 404s. I just had to change the URLs, submit a sitemap with the new URLs, and redirect the old URLs to the new ones. This impacted 85 URLs and as of now 60 are back in Google while the others are listed as discovered, but currently not indexed.

I also added this HTML sitemap just for those URLs so that they are not orphaned.

I am still puzzled by the initial Soft 404 status' however. The new URLs differ only in URL and everything else is the same.