Any chance different camcorders were used to record the problematic portions of the tape?

Many playback devices will blank the video if a sufficiently good signal is not read from tape. REW and FF display may not be subject to the same blanking criteria.

Did you ever find another player to try?

I haven't gotten any player, I got another D8, turned out to be not working, but I salvaged a recorded D8 from inside of it and I was able to test that D8 playback is fine. The tapes were probably recorded with the same camcorder per client batch.