If it is an MXF file or a clip from Final Cut Pro X that contains one of more MXF files, then unfortunately this could probably normal.
When you import a file, one of the first things that SpeedScriber does is to create an audio waveform. This allows the app to determine if any audio channels that have audio are enabled.
While reading of MXF files is possible with installation of the Apple Pro Codecs, some customers have been experiencing a severe performance issue that we reported to Apple. In our tests, a 5 minute MXF file is 8x slower to read than the same file as a .mov. This affects creation of audio waveforms and conversion to the audio-only file for uploading. If you're using short files then it might be bearable but with long files and particularly multiple MXF files in a multicam clip it can be unworkable.
However, there are signs that this issue has now been fixed. Apple have not supplied any details on when this was fixed, so it is something you'll need to test yourself.