Profile didn't say how old you are. If you're younger, maybe your span has changed. But sometimes we open our thumb hole a little too much so it feels pretty good when we first start, then as we bowl our thumb shrinks a little and now the thumb hole is too large. Some bowlers thumb shrink when they bowl, some thumbs get larger. So tape is a good start but as others have said, having your pitches checked wouldn't hurt if the tape doesn't work.
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Nicanor (Ten On The Deck)