"Special Works" at Westminster Abbey?

which week are you talking about?

I believe it’s September 17-21.
That’s when I’m visiting too.

Yes, it is the week of September 17th.

I've just looked at what's on for every day that week using the official website visit us page
https://www.westminster-abbey.org/visit-us/prices-entry-times/

and nothing is out of the ordinary. Everything is open and closed just when I would expect. They even mention the Wednesday Lates that week.

I don't buy tickets in advance so I don't know how their ticket apparatus works.

Having looked at the ticketing mechanism, I do see that that week is orange and indeed shown as partly closed. It does say to get tickets on the door for those days. I can't find anything else but I do see that for ticketing questions email needs to be sent to tickets@westminster-abbey.org and I expect that they would have your answer. There isn't a public telephone number or I would have called on your behalf.

Have you tried to email them for more information?

Thanks Nigel. The only phone number I can find is for the Chapter Office, +44(0)20 7222 5152 and "all lines are busy". waited for a while on hold but gave up. I do see the normal worship schedule for that week, so I guess I'll just show up and see how long the queue is. HH05, I hope it works out for you as well.

I am also going that week and realized it is fashion week. There is very little scheduled for the Thames festival for that week as well.
I wonder if fashion week just takes over?

Elaine, for Thames-related things to do that week, Lola posted this about concerts being performed in the bascule chamber "under" the South Tower of Tower Bridge: https://community.ricksteves.com/travel-forum/england/if-you-will-be-in-london-in-september

http://totallythames.org/event/bascule-chamber-concerts-2018

From Lola: They expect it to sell out. The bascule is the large chamber housing the counterweights that assist with lifting the bridge. Some of the concert bookings include a tour of the bascule chamber.

We were rather disappointed to show up for the Wednesday late admissions when we were there in July, only to be told the Abbey was closed to the public for a "special event." Since we'd just walked an hour to get there, we were less than amused.

Like St Paul’s, Westminster Abbey is a working Cathedral. Due to this reality it can close for special events ( think Prince Williams and Kate’s wedding and Princess Diana’s funeral)

These days with smart phones it’s easy to look at informative websites. Westminster Abbey’s website shows when it will be closed.

Always good to check in advance to not be disappointed.

It sounds like it's possible that certain areas might be restricted at various times and that by making you purchase at the door, they have a chance to let you know what may not be accessible so that you can decide at that point whether you want to go or not. Who knows, they might be filming something on those days, so you might actually get to see something that you might not normally get to see.