In one aspect, a method is performed by a content-presentation device that is scheduled to perform, at a modification start-time, a content-modification operation that comprises modifying a modifiable content-segment that the content-presentation device is scheduled to receive. The method includes receiving reference fingerprint data representing the modifiable content-segment. The method also includes making a comparison of the reference fingerprint data with query fingerprint data representing content received by the content-presentation device from a tuner device connected to the content-presentation device. The method also includes based on the comparison, detecting, within a predefined time period after the modification start-time and during performance of the content-modification operation, a mismatch between the reference fingerprint data and the query fingerprint data. The method also includes in response to detecting the mismatch within the predefined time period after the modification start-time and during performance of the content-modification operation, performing an action.