I have 6 six switches set up, all HS200 switches.

3 always work perfectly and are always connected. 

1 sometimes, when it feels like it, is connected.  Sometimes not.

1 always reports that it's offline.

I deleted the 6th from the app and was going to try and re-add it.  It WILL NOT add again no matter what I do.

I've "forgotten" connection in my wifi in my phone.  The Kasa app doesn't ask for a new password.  It just reconnects all of the above in the same fashion (3 work, 2 don't, 1 it won't find).

I've restarted the home router.

I do not know what to do at this point.  Please help.  I see almost every thread about connection is unanswered or doesn't go anywhere.

I don't know what hardware version, I don't know what firmware version, I don't how to find that information.