As with any golf club, a putter has a sweet spot. It's an area in the center of the club, around about the size of a small coin where the ball will feel its best when you hit from there. It will also roll the straightest and roll the consistent distance that you're used to seeing. Any ball that's hit around that sweet spot, on the outside of the sweet spot, towards the toe or the heel with top or the bottom, would start to react a bit differently and feel a bit differently.
So, it's quite important that when we're setting up the golf club, we line the ball really nicely right in the center of the sweet spot. It's pretty much under the line or the alignment aide that you have on the back of your putter. Line that directly up with the center of the golf ball. Then make a stroke where your hands sit very slightly in front of the golf ball that would encourage you to make a better strike down on the ball rather than scooping or hinging or flicking.
It's also really important the chest and the head stay super still over the top of the ball and just watch the club come back into a perfect impact position. One other thing I'd like to see, good solid left wrist angle. Anything that scoops or flicks from that left wrist is going to cause you lots of problems in your putting.
One of those problems would be an inconsistent ball strike. So if I can stay super still as I make my stroke and get a good consistent strike out of the middle of the putter, I can hear it hit the middle. It feels like it hit the middle and it rolls the right distance.
One other thing I would encourage you to do is practice stroking the putts around without being too conscious of your target. So don't necessarily worry about whether the ball is going in or not, that makes you get a bit too technical with your stroke, maybe just practice on empty patch of putting green and just focus on really making good solid firm contact right off the sweet spot. If you can do that, the line of your putts will improve and the pace of your putts will become more consistent.