Remember that BA places their own restrictions on CX inventory for flights departing in the next 10 days. This is to reduce fraudulent redemptions. In the past you can get redemptions for close-in departures by contacting BA directly.
Oh it has become 10 days now instead of 5 or 7 I forgot. Thanks for your information ^^
But I am pretty sure my observation is not caused by this restriction as there are still 1-2 J seats shown on BA on the same day.
Plus: some other short haul destinations such as TPE seem to be unaffected at the moment.