A few thoughts:
1- any bodyfat/lbm assessment can have quite a degree of inaccuracy
2- Too much stress/work can negatively impact those with limited recovery abilities
3- No one needs to eat 6000 cals to put on quality lbm
4- Some people drop muscle during preps and others don’t (this is a result of intelligent preps AND the individual in question)
My gut suggests to me that perhaps what you think happened might not have, and we’re just obsessing over small issues that may or may not even be accurate.