After Niantic’s Pokémon GO Fest in Chicago turned into something of a disaster – with many attendees unable to use the game at all, and others unable to login or suffering crashes – the company has laid most of the blame at the feet of carriers …

Niantic says in a blog post that unspecified ‘technical issues’ on its own server were responsible for some of the issues, and it was able to resolve these with a configuration change. But the main problem, it says, was network congestion.

The company says that it advised carriers in advance of the likely numbers and bandwidth needed, and accuses them of an inadequate response.

Niantic singled-out Sprint as a company that took action to provide the necessary capacity.

The company says that other events planned in Japan and across Europe will go ahead as planned.