At first I thought:
"Every time I use Bluetooth (I use bluezwitch or FM Radio to swich Bluetooth on or off), from then on the Skype status of my contacts is no longer shown. Must restart to get it back."
But that's not it. Must have coincided with logging out of Skype and starting listening to the radio. After logging into Skype it takes a while before statuses are being shown properly again.