As in what happened with the television series or what happened with something relating to Big Finish?
I know that the series itself suffered a severe drop in American audience figures, resulting in its cancellation by the head of ITC Entertainment. That's why there was a radical overhaul in both style and tone between the first season and its successor, it was part of a compromise organised between Gerry Anderson and ITV's New York division who had elected to hire American showrunner, Fred Freiberger as a way of appealing to American audience sensibilities. The show had its second run and (despite plans for a third year) was terminated shortly afterwards, so you basically get two completely different shows under the same banner with three of the original cast transferring from one to the other.
Both have their strengths and weaknesses, the first season had the plots, characterisations and atmosphere, but the second season got the pacing understood perfectly. I think the first year stumbles a little because the audience isn't properly primed for what to expect from future installments, it's not a space opera series, so much as it is a Gothic horror one.