Lamination peel would have typically more ragged edges along the length of it. Looks like a strike through during the original stamping of the coin to KT...any linear bit of trash, whether metal, plastic or wood could have produced such an impression at the high pressure developed during stamping. As to what happened to the item that caused it...it fell out when the coin was ejected from the press! It is very rare to find the piece causing such an error. In 1924 the machines were very different presses than those nowadays...and quality control was not as good as today.
The coin is one of a kind, but not particularly valuable. Value of $5.00 or less to an error collector, like KT. The King would have to dig through his volumes of error coins to find a similar one but is certain He has one similar in the Royal Collection.