Maybe it is the same problem as I have. I am not sure about if it happens when not connected to WIFI, but I think I only have the problem in the morning or early day. That is to say that later in the day I get home and turn on wifi, so there might be something to this...
Could this be a bug? Maybe it should be posted to the bug section?
Dm22 is mentioning something relevant as this happened after upgrading to v5. I hope this will get fixed soon