Ok, woke up one morning to about 60 new fry sucking on the glass. Over the next couple of weeks they slowly 'disappeared'.
Background: 90L tank with 3 pepper BN (2 male, 1 female and all about 3 years old). 2 old wood pieces with holes and caves. About 4 generations of swordtails (they keep breeding) totaling about 15 in number (+ 6 new fry), 9 tetra, 1 gold gourumi and 1 kuli loach. Lots of fern the fry can get lost in.
Done some reading and knew that mortality rate high, but 100%
Did see a couple of corpses on the gravel, but that's it. I thought that as they were getting more developed they would be just living inside or under the wood (I can't see because the fern hides the wood) and assumed they would re-appear when a bit bigger.
Do I assume they have all been eaten? And by what? Why?

been eaten

Grab a fry saver

ok, thanks Doug.
Is it best to have a dedicated tank for the BN then (assuming the gourami or loach done the deed)?
Or, do mama's and papa's eat their fry?

i think the gouramis are suspicios

haha, well a loach would say that hey?
Just hard to imagine a little golden gourami being pretty all day and turning into a dracula at night.
Anyway, looks like I will be getting a separate tank and moving the peppers over to it - or moving the suspects

or a fry net. Most of my cherry shrimps have gone and realizing my pearl gourami has grown

Thanks to all who have offered advice, much appreciated. Wanted to click the 'thanks' tag for each but only let me do it once.
Obviously, I have much to learn but am looking forward to it.

Well Davcat, you could not find a better place for guidance/help.

In a sense we all went through "disasters" and had been helped through by more experienced friends.
It is time for us to pass-on what we had got to others.
So, any question/doubt/etc. just ask.