System Information
Operating system: Linux-5.3.0-62-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21

Blender Version
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-07-17 07:39, hash: rB0a40c671b0b5
Worked: (newest version of Blender that worked as expected)

Short description of error
X-ray option for mesh objects in viewport doesn't work if an armature in pose mode is selected

Exact steps for others to reproduce the error
From the default start up file:
do not delete de cube
add an armature (single bone)
select the bone and switch to pose mode
clicking the X-ray button or hitting the shortcut Alt Z no longer changes the X-ray effect on the viewport for the mesh objects

The same in 2.83.2