So, I have built a Time-Traveling machine. It’s a prototype, and I’ve noticed a few kinks in the machine. If the control pad gets jammed in home mode, the universe will repeat the same day for all eternity. Also, I noticed that my machine can only go back in time within a limited range. I can go anywhere in time between ***August 12th, 1941*** and the present. This is very important to the plot of my story, and I want to give a logical reason why it is that way.

My question is, what is a plausible reason why my time machine is limited like this?