1.7.0 Client Breaking
I apologize for the lack of information and poor description; I am happy and motivated to help debug and narrow the cause since it's affecting me. First, I'm using Arch Linux which is why I received this update a few days ago. I noticed the issue and began diagnosing as soon as I rebooted. At this point I've downgraded the package back to libX11-1.6.12-1 which has been working fine for me.
I'm under the assumption that the issue is related to conflicting library usage but I cannot confirm that myself. The problem occurs when the Bitwig Studio application (a DAW) is attempting to load in a VST2/VST3 plugin (a shared library). Depending on the configuration of how the plugin is to be hosted, it either completely crashes the engine or it safely crashes the plugin with a single output to stderr:
Xlib: request 55 length 16 would exceed buffer size.
I've seen this behavior with two plugins: Pianoteq 7 (which is paid and download-gated; 6 works fine) and Vital (free, but not open-source). Those same plugins have a standalone variant which still works. They also work when loaded into other hosts, like Ardour, Carla, or Renoise. So, it's a combination of Bitwig, libX11 1.7, and Pianoteq/Vital.
I don't know where to go from here.