Map times out when using too many points (with the sort parameter)

[tinok]

When loading a map for a project with 8000 submissions the server times out with a 504 response.

Investigating the API request showed that the issue does not happen when loading fewer submissions (e.g. 3000) or when removing the sort parameter.

Loads:
https://kf.kobotoolbox.org/api/v2/assets/ahNFUSAzWQ4fpuLEjaLzmT/data/?fields=["_id"]&format=json&limit=1&start=0

Does not load (504):

https://kf.kobotoolbox.org/api/v2/assets/ahNFUSAzWQ4fpuLEjaLzmT/data/?fields=["_id"]&format=json&limit=1&sort={"_id":-1}&start=0

Possibly related to #696.

[noliveleger]

@tinok does it still happen?