BBC America is now apparently airing all 8 episodes of Broadchurch consecutively. Originally, no episode was scheduled on September 4 because BBC America decided to air all four episodes of Luther S3 at 10pm from September 3-6. However, BBC America has revised its schedule, with Episode 5 of Broadchurch now airing September 4 at 10pm (preceded by Episode 2 of Luther S3 at 9pm).
The placement of Luther at 9pm in a 60-minute slot means that episode, and presumably all the S3 episodes, will be cut to 45 minutes for broadcast. This isn't surprising, since Luther S2 averaged just 124,000 viewers, which is very low, even for BBC America. Presumably, Broadchurch is doing better than this (even 200,000-300,000 viewers would be an improvement), which is why BBC America decided not to skip a week.
[Note: As a point of reference, the first three episodes of Being Human S5, which aired over the past few weeks, averaged just 103,000 viewers on Saturdays at 10pm (in a 75-minute slot). The final 3 episodes were moved to 11pm in a 60-minute slot, preceded by Star Trek: TNG repeats (which average over 200,000 viewers per broadcast).]