Fix errors on a drupal 8 site

We have a Drupal 8.5 site that is not rendering blocks on the homepage, also getting mixed results on login page (some blocks load, some do not). The blocks load correctly on nodes. The issue first occurred when a new region was added in and a block placed into it. The content never rendered. Existing blocks were not affected, just new ones (using the default custom block type and a custom block type we created). Here’s what we’ve tried with no luck: Tried removing all HTML from our [login to view URL] file and only rendered regions to see if there was a conflict but had the same results. Created a page—[login to view URL] to try and debug, same results as default [login to view URL] Uninstalled / reinstalled our custom theme, this reset our block layout and once we tried adding blocks back in they would not render. Switched to Bartik theme, same results – something seems to be wrong in Drupal core Disabled contrib modules, same results. Installed Devel for more debug info, on homepage load we can see the blocks are being called but not rendered (Devel doesn’t say why). Before the issue occurred we upgraded core from 8.4 to 8.5 (but blocks we’re working correctly on 8.5), so we tried a rollback to our 8.4 codebase and database with the same results. Looking for someone to help resolve/research this issue.