When you play on private server you always meet lot of bugs. On my server mobs sometimes fall under textures, bot see him and try to kill, but cant. Bot can run around for hours, its a very ban danger situation.
So option one i ask to add is Move back from target. Sometimes enough to make few steps back, and bugged mob jump from texture, and can be killed.
Option two is Maximum combat time, for situations when mob absolutley bugged, bot check this timer, if bot in combat more than this value he just run to another target.
Thanks for attention and sory for my english.