Nope, I can definitely rule out any of my functions (be it RPCs or not). I made a basic attachment graph to attach an item to the character and the problem still persists.
It has to be the UE4 attachment replication.
I have some good news and some bad news.
The bad news is that I have not yet been able to pinpoint what the cause of this issue is. The good news is that I just realized that the callstack that I was getting with your project matches the callstack of a few reported crashes that some of our developers have been trying to fix.
They had not yet been able to reproduce the crash, so I updated the ticket (UE-19264) with the steps I used to reproduce the crash in your project. This crash is currently something of a priority, so the information to reproduce the crash should help them identify what is happening.
Thanks ! These are indeed good news. So I’ll be patient and do something else in the meantime. 
I also have good news and bad news:
Good: I’ve identified the crash and have a fix for it.
Bad: Fix is fairly large so might not make it to 4.9 due to risk.
Technically this is not as much a crash as an assert that is not really that correct in networked games, so I will likely make it a non-fatal assert instead for 4.9 until the real fix can go in.
The bad news is not really bad. It is great to hear that you have found the reason for the crash. And as long as you fix it sooner or later, I am very happy. 
Though I hope the fix will make it to 4.10 / 5.0 (?)… Thanks very much, Zak!
I don’t know if there has been a fix or not. Just want to let you know that the error still occurs in 4.9.
I can confirm this. I’m running in the exact same problem trying to attach a weapon to my character.
Hitting same wall.
I replaced the ensureMsg with a log, but that led a bad child index in USceneComponent::OnComponentDestroyed().
Through in a check for that to prevent it.
Now, when I detach the affected component it detaches several other components that were spawned client side.
Server side, the affect component does not share the same owner or parent component as those that will be spawned client side.
Client side, the bug causes the affected component to have the same parent as those spawned client side when it detaches (apparently).
Very confusing 
I’m looking in to this, I think the change we made incorrectly forces the attachment on clients to match that on the server, which effectively broke client-side-only attachment.
Hey Zak. Thanks for the response and your efforts.
FYI: The crash now only seems to happen in the editor. The standalone-version of my game seems to work just fine.
Hey Briandrain85-
I tested the project that you had sent to and it seems that when the client joins they initially spawn as a male character and then automatically get swapped to a female character. From my tests the crash occurs when the client spawns as a male character prior to swapping to the female. I believe it may have to do with the server / client reading the same character information, however the server is flagged as “dressed” (after putting on the shirt and pants) where the client spawns as “not dressed”. To help me confirm this could you point out which code files are responsible for spawning the characters after joining the server as well as which code files are responsible for swapping from the male to female when the client spawns?
Hey ! Thanks for your answer.
When the player gets spawned, ASomGameMode::InitNewPlayer fires and causes to set the ID set in the Event SomPlayerController::InitPlayer_Implementation, based on the parameters received while connecting to the server. The same Event Triggers a chain of functions inside the Som_PC - Blueprint:
→ ASomNetworking::CheckSession
→ ASomNetworking::CheckSession_Complete
→ ASomNetworking::CheckSession_Proceed_Implementation
→ ASomNetworking::LoadAppearance
→ ASomNetworking::LoadAppearance_Complete
LoadAppearance_Complete in turn calls the function ASomCharacter::SetAppearance, which sets (among other things) the gender of the character.
I hope that helps. Thanks again for your efforts.
Hi ,
With some of the changes that have been put into the Engine, we believe we have fully resolved this issue. Could you please let us know if you see it happen again in 4.10?
Hey ,
that is very good to hear. As soon as I am getting rid of my compiler/linker-error, I will try it out. ( VS2015 Compiling UE4.10 Preview Linker Error - Programming & Scripting - Epic Developer Community Forums )
I’m sorry to inform you that when I play inside the editor, my project still triggers the usual breakpoint (SceneComponent.cpp , Line 1393)
This was in 4.10, correct? We’ll dig into this some more.
Exactly, this still happens in 4.10 (no preview-version), but only in the editor (not in the packaged version). Thank you.
Hi ,
The sample project that you had provided for another post is now a couple versions of the Engine old. Would it be possible to get an updated 4.10 sample project to test on? If you need to provide it privately, you can reach me on [the forums][1].
Hey , I did send a PM.
Thanks. I got the message. We’ll take another look to try to find out if we overlooked something.