I too am having the exact same issue. I even tried starting a whole new game to see if maybe it was something messing up with a transfer of saved files. Nope. Will not let us change anything.

Yeah Radious updated it to be like that, theres no more forced march, I was annoyed at first but honestly the game feels allot more tense now, which is good.
If you had an army that was in forced march before the update the only way i've found of getting them out of forced march is to spawn a new general and then transfer all the units.
Then next turn raise an army with the general that was retired last turn and reinstate the legacy of that army (if you want).