Sorry about that I didn't see any scroll bars on my screen so thought it was just the one image. But it appears my chain run question was possibly right but it does pass correct side of upper jockey. The other image doesn't show that well.
I've seen and worked on a bike with such a chain run. It would not index correctly and I spotted the incorrect chain run, but it was quite subtle on viewing. Someone had installed a new chain and run incorrectly then at return for service it was not indexing on it's general check.
Edit: I have seen the others now and it looks clearly wrong side of cage tab. I'd put this as a check on one of my first replies.
MikeF wrote:Is the chain running through the derailleur correctly? It doesn't appear to be in a straight line from the top to bottom pulley, but possibly loops over the guide instead of under it.
I think you're right. I didn't notice that before.
“In some ways, it is easier to be a dissident, for then one is without responsibility.” ― Nelson Mandela, Long Walk to Freedom
I agree, I think it is (despite being a bit out of focus) clearest in this picture;
the chain appears to be running the wrong side of the tab between the jockey pulleys. This will be noisy, draggy, and will cause all kinds of troubles.
Vorpal wrote:I think you're right. I didn't notice that before.
Selective blindness like not acknowledging that I pointed this out as something to look at on 12th october. As well as after posting of image today.
old_windbag wrote:The sudden replacement of two chains in a dozen or so miles on a bike you know well would be very odd. Chain installation procedure incorrect or chain run through deraillieur incorrect( run outside of cage tab, seen that done and that bike wouldn't index reliably but would ride fine ).
+1 re the chain incorrectly threaded through the tension arm (though I have seen this done and things ran noisily but the rider had not noticed anything in use). The replaceable gear hanger look odd, cranked outwards (but looks as though it has been made that way), so the gear is mounted further out than it should be. Thus would the indexing be thrown out of kilter due to the throw being different (ie, now bigger)?
Vorpal wrote:I think you're right. I didn't notice that before.
Selective blindness like not acknowledging that I pointed this out as something to look at on 12th october. As well as after posting of image today.
I don't think that not repeating what someone else has already said is selective blindness.
I would have generally agreed that looking at chain run is something to do, but what I noticed in the photos was that the derrailleur did not appear to be parallel.
I only noticed specifically that the chain appeared to be the wrong side of the guide when MikeF pointed it out. I assure you that it is neither selective blindness, nor anything against you.
As you said, this sort of thing is much easier with the bike actually in front of you.
“In some ways, it is easier to be a dissident, for then one is without responsibility.” ― Nelson Mandela, Long Walk to Freedom
PT1029 wrote:+1 re the chain incorrectly threaded through the tension arm (though I have seen this done and things ran noisily but the rider had not noticed anything in use).
the last time I saw this fault I was MTBing with a chum of mine and his bike had the chain routed wrongly on an XT mech of similar layout. When riding behind him I noticed almost immediately that something was wrong, but he'd been riding for some time like that; from up front the noise was less apparent. I think that when the tab gets worn enough, the chain may start to snag on the tab more. I have seen them almost worn through completely. Because the chain is neatly hidden behind the cage plates, it doesn't look 'obviously wrong' when the chain is routed badly.
The replaceable gear hanger look odd, cranked outwards (but looks as though it has been made that way), so the gear is mounted further out than it should be. Thus would the indexing be thrown out of kilter due to the throw being different (ie, now bigger)?
The OP's frame has a 'direct mount' hanger. The mech is otherwise (usually) fitted with an additional bracket that fits between the mech and the gear hanger which you can see here
I've made this mistake when putting on a new chain. But I check everything is OK before riding the bike so I've never ridden a bike with it threaded wrongly. I'm not sure of the purpose of this tab. My Suntour ARX RD has much simpler cage than the Shimano ones, but I've not had a problem with it.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
MikeF wrote:I'm not sure of the purpose of this tab.
Most of my rear mechs have a tab associated with each jockey. Primarily it may be for keeping chain within cage on shifts as slack is fed through on a change. It may also act as a simple chain catch mechanism should a jockey wheel drop out. I once had lower jockey fall out on a raleigh. It appears looking at mine that this would work to some extent.
Vorpal wrote:I think you're right. I didn't notice that before.
Selective blindness like not acknowledging that I pointed this out as something to look at on 12th october. As well as after posting of image today.
Hey ho.
Well you only pointed out some things to look for and as it turns out one of those things was right. You did not point out the picture showing the mistake as you were blind to the fact there were more pictures
Anyway it doesn't really matter as it looks as though one problem has been noted and I think there is agreement on that. But no comment from OP yet.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
MikeF wrote:Well you only pointed out some things to look for and as it turns out one of those things was right. You did not point out the picture showing the mistake
When that was pointed out the OP hadn't produced images he was asked to do so by brucey I think. I asked about the history to see if pre-owned( recent purchase ) or known history as to have two chain snaps suddenly on a on a known system then faulty indexing didn't stack up. I expected OP to go and check each posters suggestions to rule each out and home in on the issue. But he did come back with the thorough history of chain events which was worth knowing in the scheme of things. Then the images.
The OP was on last night and I thought they may have gone off to check and mod the chain( he's about 7hrs ahead ). Now he could break the chain and rejoin but I'd remove lower jockey slide cages opposite direction and get enough room to get chain over tab. But if someone isn't confident then to describe that process and have them do it may be asking a lot. I'd rather not have the chain broken and rejoined again.
To be clear I am in the UK atm, and I have had my friend photo the bike. So I don't have the bike in hand so to speak so don't really have any more information than anyone else does.
I was asking with a view to potentially buying parts in the UK and bringing over there (probably in January).
I'm no expert, so I defer to those "in the know", but...
I replaced my (factory-fitted) chain with a new one. The one I bought was about 10cm longer than the old one, so I had to remove the extra links. I don't know if this extra slack could also be contributing to the problem?
Also, the rear mech hanger is designed to bend easily(ish) to protect the rear derailleur from damage if it gets bashed. It might be worth replacing it. The ones for my bike are about £12 each, and *should* fix any alignment issues if your derailleur isn't damaged.
But yeah -- get the chain the other side of the tab between the jockey wheels first!
But I check everything is OK before riding the bike so I've never ridden a bike with it threaded wrongly. 
I'm not sure of the purpose of this tab.
but I'd remove lower jockey slide cages opposite direction and get enough room to get chain over tab. But if someone isn't confident then to describe that process and have them do it may be asking a lot. I'd rather not have the chain broken and rejoined again.