Is it possible for a sharp drop in positions in Yandex and Google due to the removal of duplicates?

Question

Search Engine Optimization

In mid-December, I discovered that on the mobile version of the site (m.site.ru) there are links to the version of the page for conventional devices. Links like site.ru?ver=full. These pages went like duplicates in search engines, but after a month and a half, positions in Yandex grew and attendance also grew. I decided to change these links to the usual type site.ru. Now a sharp drop in positions and attendance is almost zero. Wrote in those Yandex support. They said that everything is fine with the site, and they will check this situation.
The question itself - can this be due to the removal of duplicates, since all links of the site.ru?ver=full type return a 404 error?

Answer 1

If traffic went to these duplicates, then they were ranked, they got an error when they were deleted, Yandex threw them out, it was necessary to either redirect or set up a canonical.

Answer 2

In my opinion, duplicates have a negative effect on ranking, otherwise it would be possible to spawn 100,500 identical pages and get traffic on them. The drop in traffic in both search engines can be caused by holidays, seasonality of queries. So you should not worry about the fact that you optimize the site by removing duplicates, most likely it should have a positive effect than a negative one.