Ponos workflow is not always loaded

This is a nasty bug on the frontend: sometimes the ponos workflow is not loaded when loading a dataimport (any dataimport, on prod, or preprod, even locally).

For instance, i just picked one dataimport in preprod, wuthin 3 refreshes, i triggered the bug:

The dataimport details are loaded, the ponos workflow url is present, but no other request come after, the display staying in "Loading..." state

Refs arkindex/requests#52