I found a solution to the KSGER Boost bug. If you disable the "Buzzer" (which makes a sound when the tip get to the set temp. or it goes to standby), the Boost works!
Somebody want to try to explain how those two functions are intertwined?
Anyway, I messaged the seller and we'll see what they propose. The internet source said they needed a new control board to fix that, since you cannot download any new firmware (if it's a software issue). Might be hardware though.
Anyway for now it's working fine other than that.