Inability to get devices working

I have one Alexa Echo plus and 4 echo dots. For the past few months they have all worked flawlessly, until last week, when my lights became unresponsive-not all of them, just one here and a trio elsewhere. All the Alexa devices work with some of the lights.
There is obviously something I am not doing right.
On advice from, I have removed and replaced both the Alexa and Mi Home apps. But the results stay the same.
What I need here is help

Please provider your xiaomi account.