By David Z. Morris
July 23, 2017 at 11:33 AM EDT

A nightmare scenario played out for Pokémon Go developer Niantic Labs. Technical glitches plagued the first Pokémon Go Fest, a festival that attracted thousands of the game’s fans to Chicago’s Grant Park. According to multiple reports, many attendees couldn’t log into or play the game.

The issues were so severe that Niantic CEO John Hanke was heckled loudly when he took the stage Saturday afternoon, with angry fans shouting and chanting “We can’t play!”, “Fix the game!”, and “Fix the servers!”

The root of the problem is still unclear. Some reports described issues with the game’s servers, while a statement made to news site Business Insider by Niantic suggested the problem might be insufficient data coverage by mobile carriers including AT&T.

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The outages were particularly enraging because the convention coincides with the rollout of a series of special in-game events and prizes. That included new Pokémon only available at the event, as well as perks for players worldwide that require collaboration with players in Chicago. The local disruption seemed to have broken those features for some players elsewhere, as well.

Niantic announced from the event stage that it will refund attendees the $20 cost of their tickets, and give them $100 worth of in-game tokens. That may be cold comfort since some tickets were reportedly scalped for far more than their initial price, and fans traveled from as far away as Australia and Europe to attend.