When the game was first released, people had little trouble finding these events and completed the associated challenges fairly swiftly. Ubisoft decided that the spawn rate was too high and decided to reduce it. With that and/or the release of the next gen consoles, people started to report that they were no longer locating these social events.
The following was posted by an Ubisoft employee known as Ubi-Valentin:
A maintenance is scheduled on 1/14 at 9:00 AM (GMT). The operation
will last for approximately 1 hour.
Tasks for this maintenance: We need to update the game server on all
platforms in order to fix an issue related to social events and also
prepare for the next Title Update.
Since this update, people have responded positively that the issue is now fixed. This forum topic highlights this fact. I have linked from the point that the UK Forum Manager quotes Ubi-Valentin regarding the scheduled update.
In answer to your questions:
- With regards to Royal Convoys and White Whales, these are found by sailing close to them (approximately within 500-750 metres of the event). Chests are found inland and will be discovered when approaching them.
- They can be found whilst moving at travel speed.
The events appear on your map as a light blue icon (chest, whale and convoy). See the map linked further down for examples.
So far, it seems visual clues can be misleading. I have spotted numerous White Whales leaping from the water, but no White Whale event spawned around this location. I came to the following possible conclusions regarding this:
- The events were broken at the time, but the visual of the whale still worked.
- The visual of the whale informs the player that White Whales do spawn in this location, but this event is not currently up.
- Just eye candy. Huge whales leaping from the water is pretty cool looking!
Social Royal Convoys will be sailing with escorts, just like the normal Convoys. Look out for groups of ships sailing in unison. Chests can be heard via the normal "secret" sound, but will probably appear on your map before hearing this anyway.
A map has been created by the community over at ac initiates, which lists many known possible spawn points. Lots of people have reported success of using this since Ubisoft's server update. It can be found here.
Regarding my own experiences. I almost completed the achievement on the PC version when it was first released (about 1 month after console release). Then nothing for a month or two and now I am starting to see them pop up again. I believe I just need to locate a chest and I am done. Hope this helps.