This is Google Penguin
This fellow is a part of Google Core Algorithm. His job is to figth with spamdexing
(creating backlinks to manipulate ranks).
In simple words he downranked sites
and pages that contains bad links.
and that's how he affected our client november 29.03.2019
You will be suprised that drop was a result of filtering just one page. But this internal page generated almost 35 % of all traffic.
Good for him that brainstorming reasons for such traffic drop tried to check all possible Google Filters
and that's how he met LinkQuidator...