Telescope build page stuck loading

[manekenpix]

What happened:

After merging #3718, the build page on staging gets stuck loading

What should have happened:

The build page should display the output of the last build

How to reproduce it (as precise as possible):

Go to the dashboard on staging, here

Edit
The error might be related to this

which is displayed on staging (which is affected by the issue), but not on production.