Intersting, it does sound like your husbandry is perfect and you've been doing a good job recording their weights. I go through a similar set of steps when something seems off. I've noticed a couple of mine are very active if I'm in the room, even during the day. Yesterday they were no where to be seen so when I checked on them last night they were both in blue so that explained their absence. Sounds like perhaps your snakes have just hit the dreaded wall and decided they don't want to eat for a while. There are lots of threads here on picky eaters, I've tried several ideas with some working and others not.
Out of curiosity what are you using to track your weights & feedings? It looks like the weights are in grams but 900 grams is only 31 ounces?