I think the eggs don't adhere well to the plastic that they were laid on. Mine would always disappear too. Once they started laying on plantleaves or driftwood the eggs would stay and hatch.
Maybe they'll get smarter & lay in the plants next time then. I thought maybe the plecos ate them. I didn't think they were guarded very closely either. Never saw dad do any work for them at all.
Any luck with another spawn yet? I'm by far no expert, but if I can offer any breeding advice, please let me know. I've had a couple successful spawns!