I seem this too at times, but in my case it is always in connection with my sync procedure copying more files over to the hub on its internal drive. It apparently cannot handle both writing data to and playing video while sharing a drive.
If I am copying to my externally attached drive on the HUB, and playing a video located on the internal drive, it handles it.
In other words, the freezes I have seen (with the catchup you mention) are related to the hub suddenly finding another task to be busy with. Copying, or updating the catalog when a file transfer ends.
So what tasks might you have it busy with?
Also, do you have the servers (Twonky and/or DLNA) enabled? Personally I ended up disabling both. Twonky because its config seems worthless, as I have been unable to have it see any files on my external drive, and DLNA for the same reason. The information passed to my other DLNA devices is most raw junk (folders).
Could it be that another PC on your net is off talking to the Hub? I have been running Network Monitor at times from my laptop and have been watching the traffic with the Hub, and there is quite a bit of scanning and “talking” to the Hub, even without any action from me.
Last possibility I can think of.. Personally I have the network shares on the Hub linked up as mapped drives from my laptop so I can access them. BUT… In that case I have to make sure to configure my Virus scanner (Norton Internet Security) on other PCs from suddenly scanning these attached network drives for virus as it will otherwise do in its standard, default tasks.
Could it be that you have another PC on your network suddenly doing its standard idle time virus scanning and hitting your Hub on the way? Which at times could make the little Hub too busy?