Thats probrably because your either using unit-group or enters region triggers... You should spawn them 1 at a time then issue them, then spawn another and issue (Best to use For Each Integer 1-100)
Also spawning at once may lag so have say a .2 second wait in it. You could copy paste it 5 times, reduce 100 to 20, then add the .2 second wait and 5 spawn, then 5 more etc like this
For each integer 1-20 do -
-Unit - Create 1 footman for player 12 at <region>
-unit - order Last created unit to right-click to <region>
-Unit - Create 1 footman for player 12 at <region>
-unit - order Last created unit to right-click to <region>
-Unit - Create 1 footman for player 12 at <region>
-unit - order Last created unit to right-click to <region>
-Unit - Create 1 footman for player 12 at <region>
-unit - order Last created unit to right-click to <region>
-Unit - Create 1 footman for player 12 at <region>
-unit - order Last created unit to right-click to <region>
-wait .2 seconds
Should work, might lag.. mes with it
