I have 3x hs100 smart plugs. One of them in the house and the other two in the outhouse. My phone cannot get a WiFi signal in the outhouse but one of the smart plugs can and the other can't. 
 

The one which can is hardware version 4.1 and firmware 1.0.3

The one which won't connect is hardware version 2.1 and firmware version 1.5.8

I set them both up in the house so they are both setup properly and if I test them in the house again they connect instantly. 
 

I wonder if anyone has any idea why one connects but the other can't?

Many thanks,

Tom