My Humax 9300 is coming up with an unusual fast-forward problem.

It seems to only happen on movies that were recorded on Film4.

I'd watch a movie and every now and then it goes into fast-forward mode for about a minute, when I attempt to playback the fast-forwarded scene, the same thing happens, it fast-forwards through it. In a movie it can happen about 5 times, totally ruining the viewing experience.

Anyone have any similar issues with their Film4 recordings?

Yes, it's been happening here too (Crystal Palace TX) - seems to be affecting Channel 4 and all derivative channels (Film4, More4 etc.) on the PSB2 MUX (Channel 26) recently. I did a full manual re-tune earlier today in the hope it might have some effect.

A list of the recordings that I have encountered which have the strange fast-forward problem.

World Trade Centre on Film4, did the skippy thing during the dark, dusty scenes in one of the fallen towers. Only happened during the dark dusty scenes so everytime it cut to these parts of the film I had no idea what the fog was going on.
Arrietty on Film4, after 15 minutes.
Insidious on C4, after 15 minutes.
Priest on C4, after 15 minutes.
Compliance on Film4, after 15 minutes.
Scott Pilgrim Vs the World on Film4, after 15 minutes.
Homeland on C4 right at the end before the credits roll up, did this on a few episodes, not all. Also some other scenes.
Hotel Rwanda on Film4, about halfway in the movie when Don Cheadle returns to the hotel in his van, there is a scene which features a lot of smoke, this is when it started doing the skipping. Also occurred in some later scenes.

I wonder if it is due to overloading the multiplex with too much rapidly changing data? Digital TV compresses the data by sending a Master frame, and then only sending the "changes since last frame" for subsequent frames; until the next Master frame resets things. By observation, it appears the Film4 sends fewer Master frames, with bigger gaps between them, than other channels.

If it is a static scene - like a newsreader reading - there are relatively few changes per frame, so lots of compression because not much "change" data has to be sent. But if it is a rapidly changing scene like swirling smoke (or waves breaking, or a rapid scan across a crowd in a stadium) then there are lots of changes between frames, so lots more data needs to be sent.