Regarding WP problems after updates

Hi! I own a website which relies 100% on SEO to be profitable. Everything was going great until I asked my developer to make some small changes like change a few lines of CSS, add security headers in the .htaccess, update the WP and the plugins. As far as I know he uses github in his work. He somehow tests if those updates will break the website and when he sees that nothing gets broken, he does the changes on the website. However, after the changes I mentioned above, the website behaves super strange. For example, i lost the main positions in Google for a day and they came back after that but the traffic did not recover fully. Also the traffic itself changed. People are now visitng the website in different hours, different pages etc. I checked, of course, if Google changed something or if i lost any of the main positions, but this was not the case. So I started digging. So far I have found that since the update we made, I have a lot of 404 errors in awstats in the hosting account. There I see that the website and google started looking for files that are not in the main file of the website and therefore recived 404 from the server. Some of those 404 were because of lack of redirects to HTTPS as well. So after days of digging and trying to undestand what is happening ( As you probably see by now, I know nothing about code and coding languages and servers and things) I found out that a few things:

  1. The htaccess file is different and the rules for redirect are not there anymore. (I made some changes to fix that now but still the question remains how the file changed if we were only changing a few lines of CSS and updating the WP…)
  2. I started getting traffic from German IPs. I checked the GEO location of those IPs and i belive the city where the traffic comes from was Frankfrt - Hessen Provice. I wonder if there are AWS servers there which are somehow related to Github and because of the complication, github, trough the servers in Germany sends those strange requests to my website. Do you belive that this is possible?
  3. Some of the files that google and my own website are looking for include github in their paths. This is very strange for me. Why can that happen?

So at this point I would like to ask you, is it possible, that my dev guy messed the things when making the changes on the website because he made a mistake in github and somehow now I have a new htaccess file, some errors in the hosting directory awstats and unusual traffic from different countries?