I see that they say
Josie’s blood and Hazel’s were fighting against each other.
That could be connected with Rh factor.
for reasons unknown and possibly as a result of our previous miscarriage - if she was Rh - and the baby she lost was Rh+, there could be some blood mixing. I had the same situation and because I didn't get the shot after the miscarriage, I got one during pregnancy so Rh incompatibility wouldn't be a problem
edit - yes, the comments also say coombs syndrome. That could slow down the baby train, right?