Took me a while to notice but E DE lost a 50 cal and Ratslayer, Cas 1 upped him by losing a 50 cal and her default weapon.
Any workarounds for this on 360?
Sorry to say, but this will be my 5th game spoiled by bugs and my last.
200 hours down the pan, I can no longer be bothered.
truly hope they deliver a patch, this has the potential to be amazing.
right now it is simply ruining my fun and wasting my time.

Can enemies make companions drop their weapons?
We can shoot weapons out of their hands so maybe they can do the same.

not impossible, but unlikely, she still had the 50 cal after being hit, it also wouldn't explain E DE losing guns.
cas is also reluctant to us other weapons i give her.
tho she cost me 14k already, not keen on buying her more guns.

I quit buying my companions weapons when I figured out that what they come with is all they really need. All I do now is give them some Reinforced Leather Armor and call it good.

Is there something that causes them to drop items in there inventory? Some people mentioned that when you go into places that require you to leave your guns behind companion weapon are taken too and they are returned to your inventory instead of there's some times.

Enemies can definitely shoot a weapon out of a companion's hands, or shoot the weapon to disrepair causing the companion to drop it because it's no longer usable (not their default weapon, just ones you give them). It doesn't happen too often, however.
But sounds more like you were hit with the casino thing, like Andaius mentioned. Occasionally for some ppl, they can be put into your inventory or disappear altogether, either during the casino checks or other stuff. I don't know if there's a way to get them back on a console.

The other thing I've noticed is if it's a weapon you gave them, if you click on it to put it in your inventory while having another weapon of the same kind on you, they'll "stack" together in your inventory but have no number in parenthesis to indicate there's more than one. So you can easily think one has disappeared. But if you click on it while in the companion inventory screen, the 2nd one will pop back on over. Happens with other items at times, too.

I noticed stacking before. when shopping.
hardly a game breaker by itself, but its far from the only bug lol.
still, the times when the game works, are awesome.

Lily dropped her default sword during a battle with a Deathclaw. It was completely busted. Fortunately, it didn't cost much to repair but had I not seen her drop it I would have never know what happened to it.

Yeah.. Cass dropped a Flamer I had nicely modded and spent some good money repairing so she could constantly use it. She's pretty damn lethal with the Flamer.

I R Sad she dropped it and I have no idea where.

I had my companions lose weapons in FO3 so this is not new. I think they can get them shot/meleed out of their hands. I lost Sydney's smg that way.

I also noticed in the final battle Boone was picking up assault rifles. He had 3 in his inventory.