So my robot partner ED-E has gone missing, and I looked everywhere for it, even in Primm where he resides if you dismiss him. This is really pissing me off because it is interfering with quests such as "nothin' but a hound dog" because I am unable to add Rex the robot dog to my party. ED-E is technically still in my party, but he isn't visibly present. I know he's in my party because people are commenting on my "flying robot" and other things can't join my party BECAUSE of him. Can anyone help?

Enter and exit a building and soon enough E-DE will be there. I do this at Doc Mitchel's house and E-DE appeared.
Doesn't matter what building you enter soon enough your buddies will be there.

Joey

check the elevators you've used recently, sometimes companions don't use them. also, backtrack to where you have been, sometimes companions just wait, even if you didn't tell them to.

I have exact the same issue as the original poster. Please update Ed-e

The Elevator in vault 22 can "teleport" lost companions to you If they are not in "wait" mode and you have complete that vault's quest.

Be warned though entering certain places such as the lucky 38 penthouse forces companions to wait. So if you lost ED E then visited the lucky 38, vault 22 will not recover it, as it will be waiting somewhere.

He should be waiting outside of the lucky 38 correct? For me he wasn't there, I picked up Raul and headed on my way but invisible ED-E is keeping me from REX. I did try the elevator thing but my guess is he is still outside lucky 38 invisible.

Try advancing the EDE my love questline and see if that has an affect if hes in your party but "invisible" maybe you could still attempt the quest somehow....at one point of the quest you will have to remove him from your party and the game will automatically do it...that could end up fixing it in some weird way...