I believe a chick has to pip to drown in shell.
Fluid in only one egg could mean that it's pores were clogged or something to that effect.. an individual egg problem.. if the rest of your hatch is going over well.
If every egg has too much fluid then highly likely the temp was off or the humidity was too high during INCUBATION (not necessarily lock down).
But for some real exacting answers.. see the following link.. *possible* cause of embryonic failure according to what day they quit and other hatch anomalies seen starts around page 51 of the following link..
https://www.hubbardbreeders.com/media/incubation_guideen__053407700_1525_26062017.pdf
Your description sounds like the first thing listed under observations on page 52. But since it was an individual problem maybe correlates to a deficiency (or shell quality) listed JUST prior on page 51.. as dead embryo >18 days.
If it's helpful or you like the other information the link contains.. consider bookmarking it for future reference..
Congrats on your babies, happy hatching!