I got this issue for several months and tried to understand how to fix by myself but it does not work. So I would like to post here to get help from the guru.
My Xiaomi Power strip (Zimi Power Strip V2) often changes to unavailable status and back to currently status (On/Off) like the picture below. I tried to unintegrated and re-integrate again by it did not work. The wifi connection of the power strip is good, I can control by Xiaomi app, but in HA it sometimes is unavailable, and I have to wait for some seconds so that it can back to normal status to control it.
I fixed this issue. I try to unplug the socket out of the socket and let it relax for a few seconds. I replug it and it work perfect again. 
I have configured correctly as instructed but still can’t get zimi powerstrip v2 into home assistant. ask for everyone’s help. Thanks!