Connecting dual 27" Apple thunderbolt displays to PC
The Thunderbolt Display does not support daisy-chaining Mini-DisplayPort.

https://support.apple.com/en-us/HT204154

I did see a report somewhere that computers that can drive two monitors over were able to get around this be inserting another Thunderbolt peripheral in the middle. I.e., Mac > Thunderbolt Display > Thunderbolt RAID > Mini DisplayPort monitor.