Semrush and Position drops after changes to website.

I work for a dental marketing company so everything is local. They have not had SEO efforts in the past relative to industry standards. So I was brought onboard to pick up the pieces and implement the Technical SEO that was lacking for clients before.

I have been working on a few clients and while I have had some wins getting clients into the map back, more recently it seems updating headings that were previously not targeting keywords, to ones that are, has made the clients drop 5-6 positions from a spot they were usually at number 1 for that very keyword. This is obviously very discouraging.

Changes I make are mostly:

• update title of page to better target keywords with volume. -add alt-text -increase keyword frequency if needed in body text. -update meta descriptions to target keyword better.

I also do NAP updating and citations all the other SEO tasks you could think of, but changes I make to the website seem to have the biggest swing in things.

I use yoast to help me with getting the green-light for a page to make sure things check out technically. Am I make too many changes to a website at once which makes google penalize me?

I do not stuff keywords. I do use the same keywords a few times, but not that the text reads like garbage at all.

I primary use SEMrush, Brightlocal, Seoptimer and Search console to track things.

How accurate is SEMrush when it comes to the the position tracking feature? Should I be using search console instead? I use SEMrush position tracker to select the keywords I want to track. I have found it most easy to use and changes show pretty fast. But I am not sure if I am doing it right.

Can anybody explain how to use SEMrush position tracking better? Am I misunderstanding something?