Inability to switch to the console using Ctrl+Alt+F1 when Mint freezes

We have two completely different computers both running Mint 17.2, one Xeon server with ECC memory and the other is an i7 laptop with _normal_ memory. Both have 8GB of RAM with default swap. Both are used to play a CPU-demanding Flash Player game (~ 50% of CPU) in the latest Google Chrome with the latest integrated Flash Player. Both have the recommended kernel installed: $ uname -r 3.16.0-38-generic The problem is, they both freeze almost every day, with an inability to switch to the console using Ctrl+Alt+F1, so I don't even know what happened. It could be important that we have AP isolation enabled in our router and SSH is not set-up.