What is your operating system?
Not material, but macOS Sierra.
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Can you repeat the problem? If so, what are the steps?
Export using dual-pass. I’ve used the settings in the attached screenshot, but my guess is this is generic for any dual-pass encoding.
Dual-pass encoding using these settings produces a huge first-pass video file. I’ve encountered this with other apps too.
There’s no need for this. The 2nd-pass only needs the log files. The first pass output should be going to /dev/null.