What happens:

When I'm trying to connect Elevator, controller block and floor with device linker I click on controller block and there are two red points. I cannot choose floor to assign.

Affected Versions:

• Thutcore: 5.19.9
• Minecraft: 1.12.2
• Forge: 14.23.5.2814
  

you have the controller in edit mode, shift right click it with an un-linked linker to get it back into floor mode.