Incorrect behavior of List Posts API for long Group mailbox conversation threads.

I am facing issues similar to the the one asked in https://learn.microsoft.com/en-au/answers/questions/5773017/unexpected-behaviour-of-list-posts-api-for-long-gr and solutions mentioned didn't work out for us. Here are my observations when I tried out the solutions mentioned there:

1. Filtering issue: It appears that the GET /groups/{groupId}/threads/{threadId}/posts endpoint doesn't currently support filtering, although the answer over there suggests it might. When I attempted this, the API didn't honor the filter.
2. Delta endpoint error: When attempting to use the /threads/{threadId}/posts/delta endpoint, it returns a incorrect Request with the error code "ErrorInvalidIdMalformed".
3. eDiscovery limitation: While I appreciate the suggestion to use Microsoft Purview eDiscovery, it unfortunately doesn't fit our current use case, as our requirement is to fetch all posts programmatically via the API.

Thank you!