Compressor ends job 80% done yet declares successful

On my 2014 Mac Mini, trying to compress an FCP video to fit on a blueray, and so send a batch to Compressor with appropriate settings (i.e., 1920x1080, 29.97 fps, avg bit rate 23.5 Mbps, max 35 Mbps, 2 pass, resize filter: linear, retiming quality: good (frame blending)) and my old mini crunches away for 5 1/2 days, and with 12 hours to go, declares it's finished successfully, but only transcoded 1 h 30 min of the 1 h 50 min of content. And no, I didn't set Compressor to only encode the first 1 h 30 min of content. Ideas?