Have the same problem now.
My Alexa worked with Yeelight LED Bulb and Yeelight Ceiling 650mm LED Lamp last 2-3 monthes.
Today I upgrade firmwares on both Yeelight for last versions (in MiHome app) and now have problems:
With Mainland China server my Alexa could discover devices, but can’t control it.
With Singapore server my Alexa couldn’t discover any devices.
I could control it from Alexa only if I set up Yeelight devices from Yeelight app. (but this app not so very useful like MiHome).
Yeelight LED Bulb firmware now is 1.4.2_0070
And I could control this bulb from MiHome app, but after update to this firmware I can’t control it from Alexa.
Could you help me please?