Muscovies dying before hatching

[hecken]

Hi, I'm hoping someone can help.
For the second time, I've allowed one of my muscovy hens to sit on eggs. It's now day 39 with no sign of ducklings so I candled the eggs. It looked like black fluid in the egg and it smelled so I took it and cracked it.
First tap, the shell came off but the membrane didn't break. It stank though. Kind of sour rather than sulfurous. So I put it into a jar to break it. Membrane was green/brown and very thick. Orange/brown slime inside the egg. The duckling was fully formed but dead. The yolk sac had some veins on it but seemed to be full of dark orange/brown gritty goo. I'll try and attach the pictures I took if I can!
This happened last time I let a hen sit. Eggs from the same hen/drake parentage have been successfully hatched by chickens by other people. So the eggs/genetics are surely sound?!
Any ideas why I can't seem to hatch ducklings?

 

[chickens really]

Could be where she is nesting or just not a good Momma?

 

[hecken]

What do you mean about where she's nesting? It's been different girls sitting both times and both times it's ended this way

 

[chickens really]

If other people can hatch your eggs from them....Then it has to be your two Hens...Are they good setters?...Are they abandoning the nest once they here Ducklings peep?....Are the nest getting interfered with?...Possibly too warm?...Lots of factors to consider...

 

[hecken]

Both girls were very dedicated. Only left the nest once or twice a day for food/poop/water. She's still sat on the nest now even though they aren't going to hatch. Temperature wise I'm in the UK so it's been probably mid teens to low twenties (Celsius) over the last month. Not particularly hot or cold. She was in a separate coop so the nest couldn't be interfered with. I'm just at a loss to why this is happening

 

[chickens really]

Yeah, I'm not sure either?.....Thats too bad....

 

[hecken]

Removed all the eggs and she's finally left the nest. I feel really bad for her