Open a schematic in Designer. Then open an other schematic in a second Designer. Now when you open the Variant Manager in the second opened Designer, it will show you all the comps and variants from the first opened schematic. Meanwhile it's also addressed from Mentor, and will be fixed in an Update or in 2.7!
For your Info: Close the VM and open it a second time, then it will be shown the right Comps/Variants.