Six competition addresses no longer have pages of their own and now redirect. Nothing was deleted and nothing is broken. The pages they pointed at were separate browse lists that have been folded into the tabs and the filter panel, so the address forwards you to whichever list replaced it.
If a bookmark or an old email link drops you somewhere unexpected, this is why. The address bar changes as it happens, with no message.
Where each one lands
/competitions/featuredgoes to the main competitions page./competitions/categoriesgoes to the main competitions page./competitions/disciplinesgoes to the main competitions page./competitions/locationgoes to the main competitions page./competitions/prizesgoes to the main competitions page./competitions/hostedgoes to Past.
/competitions/ongoing also forwards to the main page, which is the same list under a shorter address.
The one worth knowing about is /hosted
The other five land on a list of competitions you can enter today, which is close enough to what they used to show. /hosted does not. It lands on Past, which holds competitions run by UNI where every date has already gone by. If you saved that address to watch competitions UNI is running, it now shows you the archive instead. Use the main competitions page for what is currently open.
What replaced the browse pages
Category, discipline, location and prize are now filters rather than destinations. Open the filter panel from any tab and apply them there, in combination if you want, and the result is a narrowed version of the tab you are already on. That is why five separate addresses became one.
Competitions UNI lists but does not run still have their own tab at /competitions/listed, which was not affected.