Indoor & Outdoor POI Change With .22

Shot a 900 indoor .22 match yesterday and had my 208 shooting 4" low and to the left.
I had to re-zero during the slow fire portion. Don't understand why the POI changed after I had verified the zero the day before on my out side 25yd range.
Same ammo used for the match as was the day before sighting in the 208 off a rest at 25yds.
Why would it change ?

Yup! The way the light hits your front sight affects POI/POA! This can be verified by tracking your sight adjustments when shooting at different ranges facing different directions relative to sun angle. Even shooting the same range before and after noon! 

This effect can also occur at indoor ranges if the walls are painted bright white. I experienced a change from shooting on the extreme right vs. the extreme left. The same effect from how the light hits the front sight! 's

I should have mentioned that I have a Ultra dot sight on the 208. Sorry for omitting that.

Sighting off a rest in my opinion is not the best method for a pistol, your grip is probably different as is the position of the sight relative to your eyes. Low left can often be a trigger issue, hard to diagnose with watching you shoot.

Funning that most guns shoot a little low left when you take off a rest, and put it in match conditions. Others, tend to shoot low right. Go figure. The mystery of competition. The match monkey screws with the sights.

Thanks for the replies and I have mentally examined the match and tried to figure out what I did differently. 
Since I am recovering from back to back emergency surgery I could have not been fully recovered. Second thing is I have been loosing weight and my grip could have been looser than it was before everything happened. I cleaned the suspect pistol today and found my grip on the pistol wasn't as tight as in the past. My hands felt smaller in the grips so I adjust them to feel snug like they usually do. 
Now I will have to test the results when I can get to the range,