Way back at the dawn of time, there was a regular issue with low quality applications that would run XGrabKeyboard() (or XGrabPointer()), and then get stuck without releasing it again. If you can, try to log in over the network from another machine and kill application processes one by one until it releases? It’s most likely the video game (or library used by it) that has gotten stuck.
I would like to argue for the psychological safety that Google found in project Archimedes. As a manager (of any group) one of the most important things to bring is to genuinely care for your people. Also spend time on making a culture where colleagues care for each other.
At the same time, it is important to be willing to take the difficult talks and decisions early on. If you have a bully or somebody tearing down your team, take action. This also goes for interactions with the rest of the company. The task of the group is to build the best product/service/whatever for the company, and anyone aiding in that should be welcomed. Anyone hindering it needs to be stopped, regardless if they are part of the team or belong somewhere else in the company.
Finally, make sure decisions, targets etc. are there because they are good, not because of politics or ego. It may take a bit more time early on, but getting everybody on the same page with respect to how and why you (as a team) want to do particular things always pays off.
I’m not sure, there can always be other issues. But note that closing the window is not the same as terminating the application. When you close the window, the application gets a signal that it usually handles as cleaning up and shutting down. But if it is hanging, that task is not performed and resources are still held.