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I think that nobody replied because this is a really complex situation.  It could be something that went wrong with the http to https conversion.  It could be something entirely unrelated. So, a good answer to your question would require much more work that what a person might be able to give in a Q&A reply. If this was my site, my first question would be to dig into my analytics from before the first switch was made and compare to now.  What you want to find out first is what pages lost rankings.  Is this confined to a single area of the website or has the entire site been demoted.   Rankings analysis is the best way to do this.  If you don't have rankings data then dig into the same question by looking at traffic. Look at that and let us know what you find.