A lot of Freeview channels are changing this month and some are going completely. You need to rescan with whatever your menu calls
replace existing channels, if you don't "replace" it will could allocate the wrong channel number, miss out a new channel or delete an exisitng channel to make way for a new one. Some of the BBC radio channels are also affected, if you select Radio 4 it should be showing details of how to sort all this out (unless you've already lost it!). If one box can find channels when scanning but the second can't, try plugging the second box into the first aerial and rescanning. If that works take the box back to the room where it is used, it might work or it might just acknowledge the channel you've selected and say No Signal which would mean it's too weak (digital tends to either work or not, it won't take a fuzzy signal)
Sky3 (which also does holiday sales) is supposed to be going soon along with UK Bright Ideas which should be replaced by UK Gold. Virgin1 has taken over the old FTN slot so I'm expecting them to start plugging their holidays during the afternoons.