Hello. Here is the official answer from Sigma about 0.1 second shutter lag:
”We are so sorry that your fp is showing a lag between the moment of release and the actual picture. We are aware of this, and unfortunately, this is how fp works at this point. This is a display lag happening between the sensor and LCD.
I will forward your message to our engineer team, and they will check if there is something they can do to fix this. However, at this moment, we have to ask you to accept that this is how fp works.”
So maybe they will come up with something...