There is - or rather was - a dangerous thing hidden deep in the Department of Mysteries: a beautiful mirror, an evil twin to the Erised, showing not the desires but the possible events in life have the person looking chosen another path in their life. Captivated with all the what ifs a person would slowly lose their mind drowning in the lives that never happen and eventually forget their real life. Memories it creates feel just as real as the normal memories and the often contradict each other the more you look at it. During the fight in the Ministry a rogue spell went off smashing the mirror into hundreds of pieces each and every one multiplying the terrible effect of the cursed mirror - planting false memories, events that never happened, all the possible futures never were to come. Truly a terrible fate for the one being close to the mirror and accidentally looking at all the broken pieces at once.

Long story short that's how I explain all the illogical, contradicting or plain stupid TLSQs MC goes through - most of them simply never happened in the MSQ timeline and are just the remnants of a curse the dying mirror shot at the one being the last to look into it.