A large number of user sessions on the site?

Question

Nginx

Colleagues, recently discovered the problem that a large number of sessions to the site is growing, moreover, for a short time.
Most requests go into the nginx cache, and sessions are held for a long time.
And also, judging by the logs, there is a transition to our site from Yandex
https://yandex.ru/clck/jsredir?from=yandex.ru%3Bse...
but it is not clear to us what request people come with.
We also noticed that almost always the user parameter is different, let's say like this:
"Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0; MAAU; MAAU)"
Googling found out that MAAU is a vendor id or oem, moreover that they are always different:
MAAU
MAARJS
MANM
, etc.
It's not clear what's going on, can anyone share their ideas?