System Information
Operating system: Linux-5.3.0-arch1-1-ARCH-x86_64-with-arch-Arch-Linux 64 Bits
Graphics card: GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21

Blender Version
Broken: version: 2.81 (sub 12), branch: master, commit date: 2019-09-23 20:20, hash: rB5a6ab6f59468

The error appears to start from commit ce34a6b0d727bbde6ae373afa8ec6c42bc8980ce

Short description of error
A single link between nodes is not drawn when working with the nodes and a 3D editor visible. Selecting or deselecting the object in the 3D editor makes the line appear or disappear.
Found that this only occurs when the 'floor' and world axes overlays are disabled in the 3D view (but not /all/ overlays disabled). Otherwise it works as normal.

Exact steps for others to reproduce the error
From the default scene, switch to the Shading workspace tab.
In the shader editor, the line connecting the principled node and the output should already be hidden.
Re-selecting the default cube makes it reappear.
Selecting the principled node makes it disappear.
Adding new nodes and new links will show it is only one link being hidden.
"Reconnect" the hidden link and one of the others will disappear.