It does not need to be Warhammer 40K based and it has a LONG RECORD throughout history:

• Ridiculous superstitions prevail over common sense, be it anything related to "God", "Covid-19", "Whatever 1984 genocidal dictator is ruling" or "LGBT genderfluid agenda", or just about anything else
• If you disagree with someone they just kill you, send you to a struggle session or cancel you
• Routine, often organized mass murder sprees against the unworthy, unfaithful and/or the heretic
• People who are not mind-controlled warn other people to no avail
• Excessive degenerate behavior from the upperclass, mostly mass orgies (often happens during "peacetime governments" like Tsarist Russia and late-Greece/Rome)
• The proles are completely prohibited from having any pleasure or degenerate acts while the high-ups rape children (often happens in insane totalitarian regimes such as the medieval era or Stalin, although it is also happening right NOW in Europe and America; a sign of communist ideological subversion)
• Cannibalism on the rise
• Infant mortality on the rise
• Something just suddenly "switched on" and people begin to act like irrational savages in one blink of an eye

It is not just a matter of mysteriously flicking lights, people being thrown around invisibly or simply bad luck, but more like people eating each other (both metaphorically and literally) in DROVES.

Daemons are summoned by the elites, either though planned rebellions or rituals like the one in CERN, and you are already seeing some of the effects of mass demonic influence.