I have a gen 1 Flirc, it wouldn't show up in the windows app and would say disconnected etc.
So I installed the Flirc app on a raspberry pi and it detected the Flirc straight away and prompted a firmware update from 1.x.x to 3.11.0. since the firmware update, it now detects in the windows 10 app. So maybe the latest version of Flirc on windows doesn't like gen 1 Flirc's with firmware 1.x.x?