When the monster u are fighting dies, u stop doing anything what u clicked to do,
for example, im in GWD killing a minion, and at the last hit i attack another minion, when the minion dies(animation start)
my character stops (or not even starting) attacking the other monster i just clicked, but it also stops if i clicked to walk somewhere or open a door or anything

This is not happening when not clicking and auto-retaliate is turned on, but its getting a little annoying for slayer and monster hunting.

Clicking on another monster in the middle of a hit?

Can you give me a situation where I can reproduce this bug? Currently, it's a bit difficult to find out what exactly is happening for you.

best place i think is at gwd, monks of zamorak or multi areas,

just try to pick something up, or attack another monster at the end of your fight, character will stop moving for 1-2 secs and if you got auto-retaliate on it will attack again, else it will stand there until you click again,

what i usally do is check EXP gain, and click on the next monster if i know the xp i gained is a high enough hit to kill the one im fighting.