Hello

Thank you for feedback.

So, if i understand correctly, position for certain keywords drop after 30 days from #2 to #3?

Improvements that can be valid in this case:

1. Change after 30 days after content optimisation, do not look directly like related to NLP optimisation. If you optimise content and content is re-indexed changes in SERPs are in 24h (Google just understand that there is a new content and update SERPs). So change is "right now".

Solution: Optimise you content again, using as competitors only top3 pages. Re-index and check SERPs.

2. You are mentioning that one keyword drop from #2 to #3, but what about whole traffic and clicks? If you increase content score you should in general get more traffic as content is more "rich". There could be as well cannibalisation issues.

Solution: Please check GSC for cannibalisation options.

3. This can be as well "over-optimisation". We always recommend to optimise content in agile way. Where your first optimisation should be about 10-20 points higher than average of competition, or just few points higher over best competitor.
You have mentioned that your content with content score 40 was ranked #2, so i assume not a lot needs to be done to overcome #1 according to content quality.
What "over-optimisation" means? That content is not relevant anymore to specific intent as it was before.

Solution: Try to optimise content, especially with high ranking pages, with small changes in agile way.

Try to look at your pages as a traffic source from whole customer vocabulary and topical build expertise in general. Domains with strong topical authority ranks way better, even with "tiny" content.

Hope this will be helpful.