Just after Netmarble acquired Marvel Contest of Champions, it has a big headache on its hands in the form of a player revolt.

South Korea’s Netmarble acquired the Vancouver studio of Kabam, the maker of the Marvel game, in a transaction that closed last week. The studio launched a Patch 12.0 for the game, and it triggered an outburst of anger from players, who vented on sites such as Reddit. And those once loyal fans who generated more than $450 million in revenue for the game are quite mad.

“There are massive bugs across numerous characters that makes it seem like the game was not properly tested prior to this 12.0 update being released. You now have thousands of players flooding review boards, support pages, forum pages, Netmarble’s pages etc.,” said Scott Donelle, one of the players, in an email to GamesBeat. “As well as Apple support and Google play support demanding refunds by the droves.”

In a statement, Netmarble’s Kabam said, “Marvel Contest of Champions recently released a new game update as part of our ongoing efforts to maintain a balanced gameplay experience for all players. It was a substantial update, to address current imbalances and support larger future plans. However, the result was a game that changed more than we anticipated in a very short period of time. We’ve heard the players loud and clear and are taking their feedback seriously. We are in the midst of prepping a new update that will address the biggest problems and our players’ concerns. Players can visit the Marvel Contest of Champions blog later today for more information on the upcoming changes.”

The company also posted a blog message for players.

Some of the fans still remember when Kabam faced a big player revolt for its Dragons of Atlantis game in 2013.

Here’s one of the videos where the complaints are laid out.