On the browser based version of LR Mobile the Sort By Custom Order is missing the switch to reverse order.
I think that is by design. I am trying to think of a reason you would put something in a custom order and then want to reverse it. Can you give me some examples? If so, it might be a better idea to to convert this to a feature request (Called Ideas on this forum). Thoughts?
I have a collection custom order my Desktop app. I sync that collection, when I open it in the web app of LR and i choose to sort by custom order the photos are displayed in the reverse order I had set in the desktop app. No big deal if i could reverse the sort order like I do in the mobile iOS apps. For some reason its not there in the web version. You can change the sort order for date but not custom order. I thought maybe it was browser issue that the button wasn't showing.