Something I've been struggling with after upgrading from Debian 8 to Debian 9 is that when I press multiple mouse buttons at the same time (or very quickly in sequence) in games like Darkplaces (Quake 1), the inputs get discarded. This makes things like rocket jumps and monster grenade jumps difficult since the timing on those can be as critical as tens of milliseconds.
Does anyone know of a change in maybe xinput or a default parameter change that might account for this? Can I make it behave like before?