It sounds like the reception is bad at the new location.
If you are using a communal antenna on the roof, try using your own indoor amplified antenna instead, even just for the retuning, so that you pick up all the available channels.
Otherwise, if the signal is weak, then the TV won't pick them up.
Alternatively, you could try tuning in the missing channels manually.
Yes, the disappearing channels are likely caused by a weak signal.
Alternatively, a Sky box would help, since it receives channels from satellite, not the antenna.