I had this issue with my mod, with help of one guy i fixed it. The way DannyAcme described is far too complicate and long then needed. Firs you should know about this bug is that it save-file persistent. It means that if it uccur and you make save after it, this bug bug will be in this save file no matter what you do. Second you should know in bug not global, it per actor bug. Taking in account this two we can consider two posible option: 1) We see it in game and reason is still somewhere in our mods. 2) We see it in game but reason are gone - we removed bugged mod earlier but bug kepps itself in save file. To ensure that we still have a reason of this bug we should spawn new robot, type in console
player.placeatme 1c246bIt will spawn assaulttron, you also may want togle god mod with tgm so assaultron will not kill in one blow. If robot as well invisible then we should localize bug in mods. In my case reason of bug was robot race edit, so take a first look on mods that alters NPC resists, damage, behavior. Deactivate esp that you suspect, load you game and save file, spawn robot. If still invisible then it's not a bugged mod we looking for or there is another one. So don't activate it back, deactivate another one and try again load-spawn. If have realy a lot mods you may try so called binary search: disable half of esp's, try load-spawn. If bug present then it in active half, if not it in inactive half. Repeat with bugged half of mods, disable half of it and load-spawn, and so on until you localize bug. Note that after removing bugged mod already spawned robots will still be invisible because it in save file, kill them in melee or with killall console comand. New spawned robot should be fine.
