Page is not indexed: Redirect Error - not visible in Live test

For the last month I'm struggling with this group of pages google won't index on my site.

These are landing pages created over 6 months ago, specifically for one of the partners to send customers through (due to some of their own technical requirements where they cannot use the target URLs directly so a redirect is needed).

The problem in a nutshell as it is visible in the GSC reports: many pages in status "Redirect error" under the Page indexing report.

All of these pages show the error clearly - there's an issue with the redirect, which is ok if they had such issue in real life. When running the Live test which fetches the same URL - it works fine and even detects the proper canonical for the redirected page + product snippets + breadcrumbs + review snippets...

Here's the same page side by side between the google index and the live test:

When looking into the web server access logs (mine is Apache) I can see clearly that Google uses two different tools to fetch the URL for live testing and for fetching for indexing. The live tool works fine and even pulls the URL twice, once with a Mobile Inspection Tool agent (Google-InspectionTool/1.0) and then with the Desktop one.

Both end up following the 301 redirect and fetch the target page successfully.:

When searching for the real request in the access logs I can clearly see the issue - the Googlebot/2.1 agent can fetch the original URL but for some internal reason in Googlebot - it never follows the 301 redirect response and never try to fetch the target URL.

Is it an internal bug in Googlebot? Most likely not. There's probably something else in the website which blocks or doesn't allow it to follow up the redirect to this page.

For the moment the reason is not clear of why it doesn't follow up on the redirect response.

I found this other thread from last week where someone else reported the same:

https://support.google.com/webmasters/thread/455117023/url-inspection-reports-redirect-error-while-live-url-test-says-the-same-url-can-be-indexed?hl=en

I'm actively looking for possible reasons and trying different configs to work around it, but so far without luck...

Things I've tried so far:

• Make sure the redirect works from Chrome + devtools and look for any possible issues with the redirect or the target page
• Try other inspection tools to reproduce the issue (maybe with more details on the redirect issue) like https://search.google.com/test/rich-results and https://validator.schema.org/ but they both work fine.
• Try different redirect rules in Apache including removing the query params, using different target urls and changing the rules. Trying 302 instead of 301.
• Making sure the target URL is indexable (robots=noindex is not set) and robots.txt doesn't block any url in the redirect chain.
• Make sure Googlebot really fetches the 301 page right after the original 301 response and doesn't delay that for a later point in time (i.e. putting the new url into the crawl queue). I've verified from other 301 urls that the Googlebot follows the redirect immediately.