Orders to units cannot be overridden, among other issues

  1. any orders i give are always fulfilled to completion regardless of my attempts to override them. Eg: i send a batch of units to an undiscovered place, discover enemies on the way there, I cannot have them stop and fight, they’ll continue going to the spot i ordered them to and will not do anything else until they reach that spot

  2. clicking units always adds them to the “pool” (i don’t know how to call it) of clicked units, if i’m ordering soldiers about and then click on a peon, instead of unselecting the soldier units, it simply adds the peon to the pool of selected units.
    Same thing happens to buildings, click town hall after having clicked on the barracks, I have now selected both the town hall and the barracks
    (units and buildings cannot be both selected at the same time, click on a building when units are selected or vice versa will clear the selection entirely)

Sounds like a sticky shift key. Shift queues up orders and if the shift key is stuck depressed you will be unable to interrupt orders.

Unsurprisingly, this also sounds like a sticky shift key. Shift adds and removes units from the current selection. Units and buildings generally cannot be selected together which would explain why trying to shift click add them is not possible.

You will need to track down why Warcraft III is thinking you are holding the shift key all the time. Check that the OS is correctly seeing the shift key as released. Check any macro or input software is also not sending Warcraft III a shift key press event. Make sure that all game controllers are not accidently sending a shift key press event, e.g. due to shift having been tied to an analogue trigger that is unintentionally being pressed by the controller at rest.