If I was a betting man, I’d put money on the “how” element being missed or only cursorily covered in briefing. It appears there were inappropriate lateral mode and height selections, which opened the door to the subsequent poor performance.
It’s difficult to ascertain without knowing the SOPs they were operating under, but for us, a non-database NPA with a runway-aligned FAT says fly it as an overlay or RWY EXT in LNAV/VNAV. If you’re not allowed to do that, at least put the approach in so you have something to compare with the raw data. As others have said, a timing-only NPA can be incompatible with many operators' SAC requirements, especially if you are not acquiring a visual reference until <1,000R. Non-CDA also needs specific approval in my airline.
We did one of these in the sim a few years back and much of the emphasis was on the planning stage. Once you’ve got that sorted out it becomes much easier to implement.