The all time example of this "Syndrome" of course is Ralph Guldahl.
There is a story, probably by Sam Snead, that somebody had it in for Guldahl who was purportedly not the sharpest knife in the drawer, and convinced him to take lessons, from which he never recovered.
Here is a brief biography:
For a four-year period in the 1930s, Guldahl was one of the very best golfers in the world, winning two U. S. Opens and a Masters championship. Before and after that brief period, he played terrible golf and couldn't figure out why.
Guldahl first emerged at twenty-one, in the 1933 U. S. Open. Tied with Johnny Goodman, he needed a birdie on the final hole to win, a par to force a playoff. But he bogeyed the hole and finished second. Soon after that, his game fell apart and he quit in disgust. He went back to Texas and sold cars for a while, then was asked to lay out a nine-hole course. That got him involved in golf once again, and he began playing pretty well.
Back on the tour, he won the 1936 Radix Trophy with an average of 71.65 strokes per round. Guldahl became one of the few to win two consecutive Opens, in 1937 and 1938; his 1937 score of 281 was a record for the tournament. He also finished second in the Masters in both of those years, and he won the Masters in 1939, taking the lead with an eagle 3 on the thirteenth hole of the final round.
Guldahl teamed with Sam Snead to win the Inverness Four-Ball in 1940. That was his last victory. Suddenly, his game fell apart once again. He played sporadically during World War II, then quit for good.