Hello, Take a look at this URL ecobreeze.com.sg/air-conditioning-maintenance-services The keywords SERP were all improving significantly until start of this month when all of a sudden, 70% off all the ranking disappeared. The remaining 30% became worst. I tried everything - Changing content, removing video, adding and disavowing backlinks to optimize anchoring, removing high website OBL backlinks, but the ranking have not recovered. I am now wondering one thing, Google have a new update I think on December that penalize sites with poor schema data. Is that the reason why? Please advice, I am so so so desperate now.
Have you checked your site's backlinks with your competitors? In case, such as your site many new competitors can come to business and invest a lot in links and content. Compare your backlinks and content with those who are ranking well.
Try to check keyword position (im using SpySerp for that - https://spyserp.com/) and it's movement among your competitors. Based on my practice, keywords may jumps from 90+ to 9+ positions and so on, so don't worry and check SERP positions in case of need.