The golf swing has many actions that all have to happen in the right sequence and need their own time to develop. The way for all that to occur is to swing with the right tempo.
Tempo is the measure of the overall speed of your swing, the elapsed time it takes to go from takeaway to impact.
Unless your tempo is the same from swing to swing, and is the right tempo for you, your technique, no matter how well you have learned it, will not be repeated consistently if your tempo is inconsistent from swing to swing or even during the swing. Parts of your swing will be rushed, some will be delayed, others might be skipped over entirely, all because you’re swinging at the wrong speed.
The tempo that suits you best is the one at which you hit the ball off the center of the clubface most frequently. This might be slower than you’re swinging now.
This tempo is not limited to your swing. Hit every shot with the same tempo, from drive to chip to putt. Using the same tempo for every shot builds in a constant that links up all your shots and has the effect that each shot reinforces the success of the others.
If you find your swing breaking down in the middle of a round, or any other shot not performing well, especially your putting, check your tempo. I would guess get it has gotten too fast. Slow it down to where it suits you, don’t speed it up going into the ball, and you should be fine again.