There is definitely an issue with disappearing staff/vehicles when loading a game, as already mentioned here: Airport CEO Alpha 24.3 released - #170 by destinxxx
Unfortunately it occurs sporadically, only, and mostly when the game just crashed before and I try to load my autosave.
In combination with the autosave-feature that can lead to permanently corrupted save-files, as I tried to explain here: DON'T CONTINUE A SAVE ON Experimental! - #6 by sirhc80
I already sent an ingame-bug-report, but i will send another one via website with the original autosave files, as savelog.txt looks weird…