So it's easy to see why a lot of people are searching for the best way to Watch A Match Replay in Fortnite.
There's no word from Epic Games as to whether this is an issue that's being worked on, but knowing the studio it won't be long until there's some news, or a patch. Here's hoping all of the issues have been ironed out and update 4.2 will actually go live tonight, but we'll keep you posted regardless. So, as a result, "some quests may not function until the build releases". "We'll update you once we have a more accurate time frame". While you are watching the replay, I suggest have a good play around with all the various options, as it is a surprisingly robust tool.
We can expect a full list of patch notes once the update has been applied, so look forward to those at some point tomorrow morning.
This might even be why today's update has been delayed, due to last minutes problems with the feature. There hasn't been an update on when this downtime will now take place, though Epic has stated that it will be informing players when the developer has a time nailed down. The approximate server's downtime is now unknown.