Minotaur stands at the gate and doesn´t go into battle, is this a bug? Is this battle of attrition really necessary?
40-odd rounds was pretty normal for the two times I did it.
The not going through the gates is a known bug and affects several areas with turn based mode. The current suggested workaround is to turn off TBM long enough for them to get through and then you can turn it back on.
Personally I just had everyone snipe it the second time it happened to me.