I’ve realized, why my Yeelight lamp dissapears every morning.
For some reason Home Assistant has it two times in the entity list.
The only thing is, I have only one configured in the configure.yaml.
So I have no idea how to remove the other one. 
Anyone any idea?
The other comes from discovery: which has found your light. I see exactly the same, I’ve got both my manually configured and the discovered light entities.
You can either:
yeelight in discovery
you’re a rockstar, disabling it in discovery solved my problem.
I wouldn’t give a shit about it, if Home assistant wasn’t showing the lamp as unavailabe from day to day.
I had to turn off the lamp from time to time, so it can be available again.