How to not get negative score every month?
Do research. Do missions.
Even I'm doing all missions I'm getting negative score and consistently losing the game.
I don't think you do all missions.
The last save you uploaded had only 2 bases in October... you should have 8 bases in October, actually even earlier than that.
I don't understand why it happens if I have no USOs detected.
No USOs detected because you don't have enough bases for detection.
Beginner difficulty hardest than superhuman. Something wrong with balance and score calculations.
Nope, everything seems fine to me, attached my monthly scores playing on Veteran.