Dictation bug: variations of 'catch' appear without being spoken anything
A few users over in the Apple support community discussion group have brought up this problem within the past week. It has everybody stumped over there too. 
Other than your post here, and the three or four posters over there, I haven’t seen much noise being raised about this bug. 
The way it is driving it’s victims crazy, I expect this bug will raise the noise level enough to get even apples attention.
 As for me, it’s making my iPhone nearly unusable. I can’t find any way to make it happen or to make it stop happening. I can barely believe that I have dictated this entire long post without the word catch being inserted somewhere.