It is not normal behavior (that is the good news)
Bad news....I have a ton of questions
What is the device you are using? (a laptop/desktop/tablet)?
What is the operating system being used? (WIndows 7/XP/MAC)
When you have no connection....is there an error message or a pop up, any indication that something has changed either on your device or on the Sonic?
Does the Sonic display anything different (from when it is connected to when it is not)
The WiFi icon has a number (# of users connected), does it still see you connected to WiFi?
The globe = internet connection, does it still indicate connection or not?
What is the signal strength indicated on the Sonic? (to rule out reception issues)
also in that same path, does it behave like this regardless of where you are? or does it only behave poorly in certain locations?
As an FYI, you are correct there is no update for the Sonic.
We can start there and see what that gives us and thanks for helping me understand your situation.