System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68

Blender Version
Broken: version: 2.93.2, branch: master, commit date: 2021-08-03 05:58, hash: rB1eb06de2607a
Worked: (newest version of Blender that worked as expected)

Short description of error
Materials in Blender currently seem to not support more than 8 Attributes in the final material output node. Not quite sure where the problem lies but i stumbled upon it today wanting to expose 12 Node Group sliders in the Custom Property tab.

Here is a .Blend file i set up to demonstrate the issue. There is 12 circles which colors are controlled by the custom properties on the object. Only last 8 attributes are registered while the newly added ones past 8 are returned with a value of zero. When previewed individually they do give a correct value however once connected into a chain of nodes it appears they are limited to 8 inputs. Example uses Color output however i did test it on the Fac output and it gave the same results. File was set up on the Factory Settings