I was looking around at my position in standings during systests and I noticed many of the low rated participants had nearly identical code for D2. Examples:

https://mirror.codeforces.com/contest/2002/submission/275809437

https://mirror.codeforces.com/contest/2002/submission/275816397

https://mirror.codeforces.com/contest/2002/submission/275809226

https://mirror.codeforces.com/contest/2002/submission/275826393

It seems like some high rated user leaked solutions of D2 and possibly E as well ([user:NikolaT] who has a clearly plagiarized D2 ac'ed E with weird variable names), and the cheaters have started reaching GM/IM perf.