**System Information**
Operating system: Win10 x64, or Debian 10 x64
Graphics card: Nvidia
**Blender Version**
Broken: 2.93.7, 2.93.8
Worked: 2.83.18, 3.0.0
**Short description of error**
Upper GP layer without bounding to an armarture bone will disappear when the lower layer bound to armature bone.
**Exact steps for others to reproduce the error**
Blender bug, Grease Pencil layer disapear
Broken: Blender 2.93.7, 2.93.8
Worked: 2.83.18, 3.0.0
Windows 10 x64
1. File > New > 2D Animation
2. Default created by GP layers are: Lines (upper), Fills (lower).
3. Draw some shapes on both layers.
4. Change gp object to object mode.
5. In 3d viewport, create an armature with singe bone.
6. Select GP object > data properties > the lower layer "Fills"
7. Setup, Relations > Parent > Armature > Bone
8. Find that the shapes on upper layer "Lines" disappear now.
Below: unexpected result, upper layer disappear
{F12888874}
Below: temp workaround, move unbound (to bone layer) to lower position
{F12888876}
Below: sample file for bug report
{F12888878}