I was looking forward to a nice T3 lounge hop when I booked my TP run SOF-LHR, then LHR-MAD onwards (IB).
Imagine my chagrin when not only the SOF flight but all IB MAD flights moved to T5 after I’d booked!
Still, could be worse, I have a wholly T5 connection now.
SOF seems to be in and out of T3 with some frequency.